|Throughout history, this titan's marched in the vanguard. It has ever pushed forward, seeking freedom. And for freedom's sake... it fights. Therefore...it's called the Attack Titan.|
|— Eren Kruger as he prepares to pass the Attack Titan onto Grisha Jaeger|
The Attack Titan, like all the Nine Titans, was brought into the world after the death of Ymir Fritz. Though this Titan was presumably caught up in the conflict of houses between the eight Titans of the Eldian Empire subservient to the Founding Titan, it is said that the Attack Titan always fought for the freedom of Eldia no matter the day and age. During the Great Titan War as Marley gradually gained control over seven of the Nine Titans, the Attack Titan evidently never fell into Marley's hands and remained on the mainland while the Founding Titan remained overseas on Paradis Island where the First Reiss King relocated the capital.
In the year 819, an Eldian spy in the Marley Public Security named Eren Kruger inherited the Attack Titan from an unknown predecessor. During the thirteen years he held the Attack Titan, it is unknown how often he used it, if at all, until the year 832 when he brought Grisha Jaeger to Paradis Island. At the borderline, after the Restorationists were turned into Pure Titans and sent to wander the island, Kruger made use of the Attack Titan to destroy the Public Security and their ship before disposing of all evidence of the event. Afterward, Kruger entrusted Grisha with the mission to obtain the Founding Titan from the King of the Walls and passed on his Attack Titan.
Upon inheriting the Attack Titan from Kruger, Grisha used his Titan to head northwards towards the Walls, where he was found by soldier Keith Sadies of the Scout Regiment. After his arrival in Shiganshina District, it is unknown how often Grisha made use of his Attack Titan, if at all.
After holding the Attack Titan for thirteen years, Wall Maria comes under attack by the Warriors of Marley, and Grisha decides the time has come to negotiate with the Founding Titan or take it by force. Arriving at the Underground Chapel, Grisha pleads with Frieda Reiss for the sake of Eldia and the Walls, but his cries are neglected. Left with no other choice, Grisha uses the Attack Titan against Frieda's Founding Titan and overpowers her, stealing her Founding Titan and killing her along with the rest of her family, excluding her father, who escapes.
That night, after Wall Maria's breach, Grisha reunites with his son. In tears and on the verge of hysteria, Grisha gives Eren the basement key and forces him to take an injection that causes him to lose his memories. As he is injecting Eren, he tells Eren that he must get to their basement, and that Eren must learn to control his power in order to save Mikasa's, Armin's, and everyone else's lives. The injection causes Eren to transform into a Titan, and Grisha is devoured by his own son.
For five years, Eren Jaeger lived his life unaware of his possession of the power of the Titans until the year 850, during the struggle for Trost. Upon being caught and eaten by a Titan, Eren's injuries and burning desire to slaughter the Titans trigger his first transformation into his Titan form. In a nearly mindless state, Eren wanders Trost as a Titan, slaughtering many Titans throughout the day all while avoiding bringing harm to the human cadets around him. His Titan eventually exhausts itself, and Eren emerges with healed wounds.
Completely clueless as to the nature of the Attack Titan's powers, the Trost Garrison takes Eren into their custody and questions him about his Titan nature. When it becomes clear that the Garrison soldiers present cannot be reasoned with, cannon fire is used against Eren, but he successfully accomplishes a partial transformation of his Titan and protects himself and his friends from the blast. Upon Commander Dot Pyxis' arrival in Trost, the military decides to make use of Eren's Titan to seal the breached gate of Trost.
Upon reaching the boulder needed to seal the breach in Wall Rose, Eren's next transformation goes awry when his Titan falls into a feral state and attacks Mikasa Ackermann before incapacitating itself. The Attack Titan lies dormant for a short time before his friend Armin Arlelt manages to communicate with Eren himself through the nape of his Titan, and Eren regains control. Carrying a massive boulder through the streets as members of the Garrison Regiment and Cadet Corps defend him, the Attack Titan seals the hole in the Wall, securing humanity's first victory against the Titans.
Some time afterward, Eren joins the Scout Regiment after his change of custody is made official in a military tribunal. During his first month in the Scouts, the Attack Titan is subjected to a variety of studies by Section Commander Hange Zoë. At this time, the Scout Regiment discovers the dependency of the Titan's power upon a fixed goal in mind before transformation in addition to the drawing of blood. After the month's passing, the Scout Regiment sets out on the 57th Exterior Scouting Mission. However, the scouting mission is sabotaged by the arrival of the Female Titan. Within a Forest of Giant Trees, the Attack Titan battles the Female Titan, but he is defeated. While Eren is later rescued from the Female Titan, the scouting mission is cut short and is considered a failure.
A few days later, the Scout Regiment corners Annie Leonhart, holder of the Female Titan, in Stohess District, and she transforms into the Female Titan once more than a last resort. After some hesitation, Eren battles her a second time with his Titan. When he is overpowered late in the battle, his Titan undergoes a sudden change and catches fire in a berserker-like fit of rage. The Attack Titan gains the upper hand over Annie, though the assault comes to a close when Annie uses her hardening ability to encase herself in a crystal-like substance to avoid capture.
The next day, Eren joins the Scout Regiment's efforts in dealing with the sudden Wall Rose invasion. At this time, Reiner Braun and Bertholdt Hoover reveal their respective identities as the Armored Titan and Colossal Titan. When the two transform into their Titan forms, the Attack Titan battles the Armored Titan. Despite initial difficulties, the Attack Titan gains the upper hand and nearly defeats the Armored Titan until Bertholdt's Colossal Titan cuts the battle short in a last-resort effort to capture Eren.
During the week after the invasion, the Scout Regiment goes into hiding as Military Police action against them dramatically increases. Hange Zoë runs experiments on Eren's Titan in the wilderness, where they discover that Eren is unable to harden his Titan body. Some time later, Eren is captured by the Rod Reiss, who desire to feed Eren to his daughter, Historia, in order to return the Founding Titan to the royal family. While captured, Eren gains memories of his father using his Titan to devour the Founding Titan, and slaughter the majority of the Reiss family. Eren also sees the moment where he ate his father to gain the Power of the Titans.
During Eren's rescue, he ingests a bottle labeled "armor," and gains the ability to harden his Titan's skin in a manner similar to the Titans inside the Wall and Annie's Female Titan. Eren uses this new armor ability to protect squad Levi from the collapse of the Underground Chapel set in motion by Rod's transformation. The next morning, Eren uses his powers again to shove gunpowder filled barrels into the mouth of Rod's enormous pure Titan. The resulting explosion blows apart its body and allows squad Levi to finish the job.
The Attack Titan's hardening ability becomes an important part of Erwin Smith's plan to retake Wall Maria. Upon the Scouts' arrival to Shiganshina District, Eren switches to Titan form and uses his ability to successfully plug the hole in the Wall, then reverts to human form in order to hide from the Warriors suspected to be preparing an ambush.
The mission is interrupted by the sudden appearance of the Beast Titan and the Armored Titan, beginning the battle of Shiganshina District. The Attack Titan battles the Armored Titan a second time, with this duel ending in Eren's favor due to his new hardening ability.
Before Reiner can be killed, Bertholdt comes to his rescue and wards off the Scout Regiment soldiers before transforming into the Colossal Titan. Eren attempts to attack the Colossal, but he is kicked into Wall Maria and is incapacitated.
Armin once again brings Eren back to his senses and formulates a plan for him to defeat the Colossal Titan. As Armin distracts Bertholdt, Eren's Titan falls to the ground near the breached north gate of Shiganshina and hardens itself. Thinking that Eren has succumbed to a concussion, Bertholdt thinks nothing of it, but soon realizes that he is seeing the hardened shell of a Titan, and at that moment of vulnerability, Eren in human form strikes at the nape of the Colossal Titan, pulling Bertholdt out of his defeated Titan form.
- The Attack Titan shares the same Japanese name with Attack on Titan: 進撃の巨人 (Shingeki no Kyojin?).
- The Attack Titan is the only one of the known Nine Titans that has not been confirmed to have any unique abilities on its own, but it can be given the hardening ability with a specialized serum.