|I'm certain that Eldians are the descendants of devils. And I'm certain...that we too are devils.|
|— Magath agrees to Willy Tybur's plan|
Formerly a commander (隊長 Taichō?) of the Eldian Unit of the Marley army, and before one of the chief overseers of the first Warrior candidates during their training, he later led the Eldian Warriors in the Marley Mid-East War against the Mid-East Allied Forces, playing a key role in Marley's victory.
Magath was an older man with light eyes and a thin beard, mustache, and short thinning hair. He had visible wrinkles from age but an overall healthy build and appearance. Like his fellow soldiers, he wore the standard Marleyan soldier uniform consisting of a light jacket and pants with a black clip at the collar, supply packs on the hip, suspender straps, a hard hat with a black stripe around it, and tall combat boots.
Theo Magath was extremely dutiful, and most of his personality and choices revolved around what he believed was his duty as a soldier of Marley. Even though he, as a typical Marleyan, was prejudiced against Eldians, valuing the lives of the Marleyans above the Eldians and being angered when one questions his orders, he was willing to put his opinion aside and let the Eldians under his command speak, in case they might have something useful to add to the current situation, such as Colt Grice and Zeke Yeager.
He readily accepted Willy Tybur, an Eldian, as his superior after figuring it out, and accepted the fact that he will soon inherit the role as the general of Marley's army more out of a sense of duty to his commanding officer and homeland than personal desire, even though Willy had presented it as an offer instead of an order. He even states that the army does not belong to him, but the nation itself.
Many of his decisions made him appear as though he considered the Eldians under him as expendable pawns and uncaring towards their lives, such as deciding to sacrifice 800 Eldian soldiers to destroy the anti-Titan artillery, while keeping two holders of the power of the Titans and the Warrior candidates safe. However, he mostly went with this course of action because it is most beneficial to Marley, as he wanted to keep Warriors, as well as the Warrior candidates, out of harm's way since most of his nation's might comes from the Titans, being aware of the other nations' technological superiority. Compared to other Marleyans, he was quite tolerant of Eldians, willing to hear them speak, did not appear to get physical with them, and even showed genuine concern not present in other Marleyans, noted when wishing a safe return to the Warriors who were leaving for the Paradis Island Operation. Despite this, Magath continued to view the Eldians on Paradis as enemies of Marley and Eldians overall as lower class citizens until just after the Rumbling occurs. He still wished to save Marley, but acknowledged that the crimes of the older Eldian Empire should not be forced upon those currently living on the island.
Magath proved himself to be a very cunning and perceptive individual, managing to figure out the Tybur family was secretly ruling Marley, and seeing through the country's deceptions in the various forms of propaganda. He also spoke with a certain level of dry wit, stating to Willy Tybur that the statue of Helos was the true spirit of Marley, due to it being completely hollow.
While the details of his rise to power are unknown, Magath has been a member of the Marleyan military for over twenty years. Early in his career, Magath was considered one of the best artillerymen in the Marleyan military. Afterward, he acted as one of the chief overseers of the Warrior program, evaluating the performances of each individual Warrior candidate and selecting the top performers to be inheritors of the power of the Titans. By the early 840s, Magath had achieved the rank of commander.
One day during the early 830s, Magath was supervising a training session of the Warrior cadets with Tom Ksaver, the Beast Titan at the time. While the two were watching the cadets training, Magath noticed a cadet trailing behind the others and then commented that this Warrior in particular, Zeke Yeager, did not seem to have the guts to become a Warrior.
Magath was then seen belittling Zeke in front of all the other cadets, telling him that Marley needed real men as Warriors, and that they would never give the nation's precious Titans to an Eldian like him. Some time later, during a public training demonstration, Magath noticed Zeke was among them. Belittling him once more, Magath insisted that Zeke did not have a place in the training and that Marley did not need him.
Magath would remain overseeing the Warrior program for several more years and took part in the ceremony that saw Zeke Yeager inherit the Beast Titan from Tom Ksaver. With the tenure expiring soon for the holders of the remaining Marleyan Titans, Magath was among those deliberating who the next inheritors from the most promising of candidates should be; he would ultimately select Annie Leonhart, Bertolt Hoover, Marcel Galliard, Pieck Finger and Reiner Braun to receive the Female, Colossus, Jaw, Cart and Armored Titans. In the year 843, during the final battles between Marley and an enemy nation, Magath was among those who witnessed the enemy's destruction at the hands of the newly trained Titan Warriors. Magath admitted that while they were more effective than their predecessors, he expressed some resistance to the decision of entrusting the upcoming Paradis Island Operation to mere children. Two years later, he was given orders to keep Zeke and Pieck in Marley as deterrents against enemy nations and the rest were to be sent to Paradis Island for the mission. He debriefed the Warriors and departed with Annie, Bertolt, Marcel and Reiner to the border of Paradis Island. Magath gave his final debriefing to them before departing, hoping they would all return alive with the Founding Titan.
About four years after the failed Paradis Island Operation, Magath led an 800-Warrior unit against the Mid-East Allied Forces at the battle of Fort Slava. When the Warriors' trench line could advance no further towards the bunkers around the fort, candidate Colt Grice suggests to Magath that both the Jaw and Cart Titan should be used against the Allies. Magath refuses this suggestion, pointing out the Allies' anti-Titan artillery and the great risk of losing their Titans against it. Candidate Gabi Braun offers to use a bundle of grenades to destroy the armored train carrying the artillery, but Magath refuses to waste an Eldian soldier needlessly. Gabi becomes sarcastically coy with the commander, wondering why her life is more important than the 800 others in the unit, and Magath eventually gives in and sends her out. Once Gabi succeeds in destroying the armored train, Magath sends out Galliard to attack the fort.
As Galliard and Pieck lead a charge against Fort Slava's defenses, Magath remains behind with Colt and reviews their strategy. Colt correctly guesses that the Warriors should retreat and block escape routes while Zeke's airborne attack continues the assault. When the time comes for Zeke to make use of his Beast Titan to rain mindless Titans down upon the fort, Commander Magath, and the Warriors watch from a distance as Marley's Titans complete the assault on the fort.
Some time afterward, the leaders of the Marleyan military convene to review the world's reaction to the end of the war between Marley and the Mid-East Allied Forces. Commander Magath explains to the outraged general of the military that the technological progress of the world is overcoming the power of the Titans. Magath states that Marley has been too reliant on the power of the Titans, leading to an inferior navy which barely survived the war. In the meantime, other nations have been working hard on developing weaponry to overpower the Titans. Magath proposes that with the progress being made with aerial weaponry, Titans may become useless in future wars. Zeke proposes that Marley must acquire the Founding Titan to gain full mastery over the Titans as soon as possible while focusing on developing conventional weaponry, an idea which impresses the general.
After the meeting, Magath meets with Zeke and Colt, congratulating Zeke on his conduct during the mission. He takes the opportunity to inform Zeke that over the past three years, a total of 32 scouting ships sent to Paradis Island have disappeared without a trace, and he asks for Zeke's opinion on the matter.
Zeke recalls that four Titans, the Attack Titan, the Founding Titan, the Colossus Titan, and the Female Titan, are still located on the island. He proposes that at least two Titans, one of them being Eren Yeager's Attack Titan, have sunk their ships. Magath suggests that battleship support will be necessary for an assault on the island, but Zeke informs him of the existence of anti-Titan weapons on the island, as well as the Ackerman clan which poses a serious threat to their future efforts.
Magath later departs on a train towards Liberio. Despite the Eldians at the back of the train making a loud ruckus, Magath allows them to continue with the celebrations, noting it is only for a single night. When the train reaches the Warriors' hometown, Magath gets off the train with the others and escorts the Eldians into the internment zone.
Whilst the Eldian Warriors hold a private, unofficial meeting, Magath is a part of a team tapping the meeting to test the loyalty of the Warriors. He is slightly disappointed by Zeke's comment that insinuated that the meeting was being tapped.
Magath is paid a visit by the Tybur family and is greeted by the family's current head, Willy Tybur. Speaking privately, Willy asks Magath if he is able to tell which Tybur is currently in possession of the War Hammer Titan, but Magath insists he cannot. Magath notes that his leader at headquarters left earlier that day after receiving orders from his superior, and because of that, Magath is now speaking to Willy in this place. He asks if the timing is truly unrelated.
Willy declines to answer, claiming that he came to see the statue Helos, the Marleyan hero who slew the Devil of All Earth. He praises the figure as the spirit of Marley and Magath agrees, remarking that the statue is hollow. Magath intends to reinstate conscription for Marleyans, so war is something more to them than something they read in the newspaper, though he doubts it will be enough to stop Marley's self-destructive march to war. Under the assumption that he is speaking to the true power behind Marley, Magath tells Willy that it is too late.
Noting Magath's insinuation, Willy reveals that the Tybur family is, as Magath suspects, the true ruler of Marley. However, he insists that Marley's penchant for war has always existed, and that the Tyburs merely allowed the nation to do as they wished as penance for their suffering under Eldian rule. With the passing of time and the obsolescence of the power of the Titans, Willy is concerned about Paradis Island. Commenting that Marley needs another Helos, Willy entreats Magath to work with him. Shortly afterwards, Magath is chosen to become the next general of the Marleyan military when the time comes.
One month later, Magath is present at a meeting where the Warriors discuss potential Paradis Island invasion strategies with their Marleyan superiors, though the meeting does not end well. Later that day, he meets with Willy Tybur and hands him a notebook explaining the state of his "house," which Willy notes is in need of "demolition." Willy congratulates Magath on his inevitable upcoming promotion, and the two discuss the military and their country. Magath notices Willy's trembling hands as the latter expresses the burden that comes with his position of power. Changing the subject, Magath informs Willy that some "posts" in his house were still usable, and he has come to learn that "mice" have invaded his home.
As Magath and Willy head to the festival, they discuss the security involved in order to protect Willy and the officials present. Magath does not think it will be possible to defend everyone given that Willy wishes to be on stage and to bait their enemies with as many military officers as possible. Though Willy says Magath can limit it to the useless ones, leaving him free to rebuild the military with whoever he likes, Magath is concerned about the number of people who will die. This is not the war he is used to. They do not know their enemies, how they will attack, and there will be massive crowds of people.
He tells Willy that if he goes ahead with this, he will die, and he is too important to lose. However, Willy confides that if he escapes and is not among those sacrificed, the world will not listen to what he has to say. Magath agrees to go along with the plan, admitting that Eldians are devils, but so are he and Willy.
On the night of Willy's production, Magath brings an armed team atop a nearby building to observe the crowd for any suspicious actions. He takes a report and realizes that the soldiers who have gone to retrieve the Warriors have disappeared and the Warriors are missing as well. Magath has the reserves mobilized to search for them and notes that the event has begun. When the Attack Titan suddenly bursts out of the stage and murders Willy Tybur, Magath watches in shock as it begins a mass slaughter of the Marleyan military's top brass.
The War Hammer Titan emerges to combat the Attack Titan, but is quickly overpowered while Magath's subordinates rush to his side and remind him of their dire situation. Paying little heed to their reports, Magath fires his rifle at the Attack Titan to commence Marley's counterattack against the invader. Noting that their task to defeat the Paradis Island Eldians has been made much easier, he orders his men to head to their battle stations. The War Hammer soon regains the advantage and impales the Attack Titan on a massive pike of hardened flesh, though Magath reminds his soldiers that he dealt the first blow to their enemy.
During the battle between the two Titans, Magath's troops fire a barrage of anti-Titan artillery at the Attack Titan. Koslow worries that they will lose the Founder if they kill the Attack Titan now, but Magath insists that Marley's goal to take the Founding Titan has no place in their policies anymore. The age of the Titans is coming to an end, and ridding Paradis Island of the Founding Titan will deal their enemies a crippling blow, and Magath notes that the War Hammer Titan appears to hold a similar disinterest in taking the Founder.
The War Hammer Titan quickly overpowers the Attack Titan, forcing Eren Yeager to reveal himself. Magath and the others watch as the War Hammer prepares to deal the killing blow, when suddenly Eren calls for Mikasa to finish off the War Hammer. She strikes the War Hammer from behind with eight explosive rods, destroying the War Hammer's nape. As Magath is caught off-guard by the maneuver, other soldiers land on the rooftop and begin a firefight with the Marleyan troops.
Magath and his troops escape the firefight into the shelter of a civilian building where Magath alerts all the nearby army and navy forces, ordering for the Liberio internment zone to be closed off. Magath notes to himself that just as Willy Tybur had planned, all the world would soon join the war against Eldia, though he wonders why the Paradis Island troops are proceeding with their plans knowing of this as well. His thoughts are interrupted when a bomb is sent into their room, forcing them to relocate.
Commander Magath and his soldiers relocate to the plaza where the Attack Titan locates the true "body" of the War Hammer Titan: a crystal encasing the younger sister of Willy deep beneath the ruins of the stage. He watches helplessly as the War Hammer is about to be eaten until Galliard's Jaw Titan arrives at the scene, attempting to bite into the Attack Titan's nape to take the Founder until the Ackerman cuts his jaw muscles. Magath and his troops remain hidden as the Cart Titan and Beast Titan arrive at the plaza to battle the Survey Corps. While the Survey Corps and Warriors engage, Magath is joined by Falco Grice. He initially tells the candidate to escape, but is told that Reiner is unconscious at the back of the plaza. Gabi also joins the Marleyan troops, while Falco states that Eren Yeager was responsible.
At the nearby harbor, there is an explosive transformation that destroys the docking fleet. Magath orders his troops to get away, knowing that only the Colossus Titan could be culpable, but the shock-wave from the blast throws the group to the floor. After the Ackerman takes down the Beast Titan, Magath and the others watch in horror as the soldier drops an explosive into its nape, staring at them all the while. As the attack turns to the Cart Titan, Magath grabs onto Gabi when Falco runs to the Titan's side, begging the Corps not to shoot.
As he and other Marleyan soldiers repel the Corps, Magath orders Gabi to assist Falco in rescuing Pieck, who had come out of her Titan's body unconscious. They later take refuge inside a building, and Magath and the others witness the arrival of an airship coming to aid the Survey Corps. After the airship escapes, he returns to check on Pieck who then explains her suspicions of the mysterious soldier who trapped her and Galliard.
As Marley recovers from the battle, Magath oversees cleanup operations where he has the remains of the Beast Titan investigated. Zeke's limbs are recovered but his body is missing; Magath pieces together that Zeke must have faked his death and escaped with the forces from Paradis. He calls an emergency meeting and summons the remaining Warriors; detailing his recent discovery, he believes that Zeke has been working with the enemy for at least four years. He announces that a global military alliance is forming and will conduct a scorched-earth operation to utterly destroy Paradis Island in roughly six months. However, Reiner insists that is what Zeke is likely anticipating and proposes that Marley launch a surprise attack immediately. 
Stationed aboard an airship with Reiner, he leads a fleet of airships from Marley that soon passes into Shiganshina District; after receiving a smoke signal from Pieck and Galliard informing Magath that they have engaged Eren, Magath orders his forces to launch their attack. He takes a group of soldiers and parachutes into Shiganshina, where he meets up with Pieck and Gabi. After chastising Gabi for putting herself in danger, Magath discusses with Pieck the likelihood of Eren using the Founding Titan against them. Gabi's revelation that Paradis now has a Titan of royal blood according to Zeke leads Magath and Pieck to conclude that Zeke himself is probably this Titan; realizing this explains how Zeke was able to transform Eldians into Titans by screaming, Magath orders his forces to prevent Eren from coming into contact with Zeke and activate the Founder. Manning the anti-Titan artillery harnessed by Pieck, Magath declares that they are going to have Eren devoured and take back the Founder.
Pieck takes Magath to the top of Wall Maria, where he will have a clear shot of the Attack Titan with the artillery. He manages to score a direct hit to Eren's head with his first shot, impairing Eren's motor functions. Magath fires a second round into his head to further cripple him, intent on forcing Eren to use up all of his strength regenerating from his injuries. However, as Reiner struggles to devour Eren, he is knocked away by debris thrown by Zeke, with Magath displeased to see the arrival of the "Boy Wonder." Magath and Pieck are immediately put on the defensive by Zeke's rock throws; despite Pieck's reservations, Magath insists they continue and will take out the Beast Titan themselves. However, before Magath can fire an artillery round at Zeke, he and Pieck are set upon by the Survey Corps soldiers who arrived with Zeke.
To trick the soldiers attacking them Pieck exits her Titan form, causing it to begin decaying. The resulting lull in attacks from the enemy allows Magath enough time to properly aim the artillery on the Cart Titan's back and score a direct hit on the Beast Titan, destroying part of the right shoulder and nape. Although the Beast Titan is knocked off the wall, Magath realizes that his shot did not fully destroy him and orders his forces to finish off Zeke before he can recover and utilize his ability to transform the Eldians, who had ingested his spinal fluid, into Pure Titans.
Magath scores another hit on Eren before he and Pieck come under attack from Floch's soldiers. After repelling the attack, Magath fires on Zeke again before Armin fires a Thunder Spear at him, destroying the anti-Titan artillery. Magath miraculously survives the explosion only to witness the awakening of the Wall Titans.
Magath also survives Wall Maria's crumbling and retreats with Pieck. Pieck notices that Marley's airships are leaving the island and Magath suggests that they are going to warn Marley of Eren's impending attack. As Magath assures Pieck that they will continue fighting without reinforcements, the two are caught off guard by the arrival of an enemy soldier. Magath negotiates with the soldier and their companion Levi Ackerman. Impressed with Levi's willingness to put himself in danger to speak with them, Magath agrees to work together with the two to bring down Zeke. Together they come up with a plan to have Pieck retrieve more soldiers who will agree to help them from Shiganshina. As part of the deal for helping rescue Hange and Levi's comrades, Magath orders that Yelena also be brought to him.
After the rest of Hange's soldiers arrive, with Reiner, Falco, Gabi, and Annie in tow, the group all share a meal together. Magath points out that Eren's plan succeeding would only benefit Paradis and asks if the soldiers have finally realized that helping the outside world is the just thing to do. Jean Kirstein, frustrated at Magath's attitude, claims that Paradis has only been trying to make the world stop treating them like devils and Magath retorts that all of the world's concerns have been proven to be well-founded thanks to Eren. Jean argues that Eren is only acting extremely because of the horrible acts Marley has committed against Paradis and Magath reminds him that it was in fact Eldia which oppressed Marley first, before the Eldian Empire fell.Once hostilities have calmed down, Magath reveals that he intends to find out where exactly Eren is heading by interrogating Yelena. His attempts at getting Yelena to cooperate prove to be fruitless, as Yelena begins antagonizing the group and trying to turn them against each other rather than help them.
The next day, the group goes to Paradis' harbor to use the Azumabito clan's airship to pursue Eren across the ocean, only to find that the harbor is occupied by Yeagerists. Magath is undeterred by the obstacle, but Hange's realization that Eren has already reached Marley sends him over the edge. Enraged at his homeland's peril, Magath breaks Yelena's arm and threatens to continue torturing her until she agrees to tell him where Eren's exact location is. Hange talks him down and Magath, in despair, apologizes to the Eldians for antagonizing them the previous night. Magath apologizes for everything they have been put through, but begs them to, for the time being, tolerate the actions that he will have to take to save his country from danger. To his surprise, the Eldians agree to help fight the Yeagerists at the harbor if need be.
The group begins a plan to try to trick the Yeagerists into handing over the Azumabito mechanics without a fight, with Magath on standby with Hange and Jean in case fighting erupts. When the Yeagerists are alerted to their presence, Magath helps escort the Azumabito to the basement of the building they are being held in so that they will be safe from the impending battle.
While sheltered, the Azumabito mechanics inform Magath and Hange that it will take them at least half a day to prep the flying boat for launch and Magath is left devastated at the realization that it will be impossible for them to save Liberio. Kiyomi reveals that they might be able to speed up the process at an island off Marley's coast, Odiha, and the group agrees to take the mechanics there.
Magath escorts the mechanics to the boat, firing on any attackers and ordering Reiner to defend them from incoming thunder spears. They reach the boat, where Connie gives Magath an injured Armin to watch. Magath takes Armin inside the boat to heal and helps Gabi give their allies covering fire from the boat. The boat is readied, but Falco loses control of his Jaw Titan form after transforming to help and Magath is forced to remove him from his Titan and carry his unconscious form to the boat.
As the ship leaves the harbor, Magath chooses to stay behind, intending to destroy a Marleyan cruiser left at the harbor so that the group cannot be followed. As he makes his way to the cruiser, he is spotted by two Yeagerists but is saved by another Paradis soldier who offers to help him. They barricade themselves inside the cruiser's storage room. As he prepares to detonate the ship, Magath tells his ally that he will be remembered as a hero for helping save the world. The man tries to compliment him likewise, but Magath refuses to accept praise because of his background in the Marley military and then expresses regret for his Warriors being unable to live normal lives. Still, the man commends him for his actions and the two exchange names before detonating the ship.
- Zeke Yeager - Magath was overseeing the Warrior program when Zeke joined and initially saw him as worthless and not worthy of becoming a Warrior. He would often belittle Zeke's efforts but eventually, Magath became impressed with Zeke's consistent efforts and began to view him in a more positive light after Zeke exposed his parents as the leaders of the Eldian Restorationists; Magath would ultimately select him to become a Warrior and the next inheritor of the Beast Titan. While he expected Zeke to display the respect towards Marleyan authority that would be expected of any Eldian, he nonetheless openly expresses how impressed Zeke left him with his words and actions. He was willing to disclose valuable military information with Zeke, and even accepted his advice on the issues faced by such matters. The relationship between the two was severed after the Raid on Liberio when Magath realized that Zeke was actually working against Marley. Magath was clearly agitated by Zeke's betrayal, failing to keep a level-head while engaging him in a shootout and saying that he would punish Zeke himself.
- Pieck Finger - Like with Zeke Yeager, Magath had expressed how invaluable Pieck is to the Marley military effort despite her Eldian heritage; this is often by observing how Pieck is able to use her mind and intellect to develop tactics against the enemy on a much quicker level. Despite the recent betrayal of Zeke, Magath trusted her so much that he personally went with her to fight both Zeke and Eren within Shiganshina instead of sending a soldier in his stead.
- Willy Tybur - While only having known Willy Tybur personally for a month, Magath developed a strong trust with the nobleman. Very soon after their first meeting, Willy understood that Magath possessed more knowledge of the truth behind their nation than he let on, and the former was willing to discuss the nature of the Tybur family's authority and even the possession of the War Hammer Titan with him. Together, the two had conspired to bring about great changes for their nation, which Willy believed is in need of another "Helos."
- Colt Grice - Magath looked down on Colt for being an Eldian, as he did with all others of that nationality. However, he showed some value for him as a soldier, being concerned for his well-being when he rescued his brother Falco from enemy fire and listening to his ideas when he pitched them, even if he was going to deny them.
- Eren Yeager - As the current holder of the Founding Titan, Magath viewed Eren as the biggest threat to the safety of Marley. After Zeke's defection, Magath realized that both Yeagers have the potential to destroy Marley; thus, Magath was prepared to do anything and everything possible to kill Eren and take the Founding Titan away from Paradis and hand control of its power to Marley.
- Keith Shadis - Magath expressed gratitude to Keith for his efforts to stall the Yeagerists and even thought that he would be viewed as a hero in the future.
- Magath tied with Porco Galliard for twenty-fourth in the Third Character Popularity Poll.
- There is an inconsistency in Chapter 91 in which Magath appeared in several panels wearing the Eldian collar badge instead of the standard black clip.