Kenny Ackermann (ケニー・アッカーマン Kenī Akkāman?) was the captain (隊長 Taichō?) of the Anti-Personnel Control Squad in the Military Police Regiment. Kenny was a former serial killer who would slit his victims' throats, considered by some to be an urban legend known as Kenny the Ripper (切り裂きケニー Kirisaki Kenī?). He raised Levi Ackermann and taught the latter as a child how to survive.
Kenny had shoulder-length brown hair, a thin beard along his jawline, and gray eyes. He was a very tall and slim man who appears to be well-built. He had the appearance of a middle-aged man with wrinkles around his eyes, which are small and piercing. He wore a simple white shirt and black pants, along with a fedora hat.
When he was younger, Kenny had a more defined face and much fewer wrinkles. He did not have a beard but he still had dark sideburns. Also, his hair seemed to be slightly longer. He used to wear a long coat, dark trousers and shoes, a white button shirt and another hat.
Despite his previous life as a serial killer, Kenny appeared to be a rather jovial man. Even in the midst of battle, Kenny had no trouble remaining cheerful, seemingly taking pleasure in taunting his adversaries. He had also proven to be rather animated in how he behaves, yelling and making a scene when he corners Levi in a tavern, and throwing furniture to try to provoke Levi. Despite this, he could seemingly control himself when he needed to, being able to sneak up on his targets without them noticing him.
Kenny had also proved himself to be very cold, showing no emotion when he kills his prey. He also seemed to hold very little emotional attachment to those close to him, having no qualms with trying kill Levi, despite having raised the man as a child.
Kenny's wanted power, and his personality was molded around this goal. He was a ruthless individual who did not hesitate to do anything to get the job done, including murdering children or betraying his allies. He operated with utter professionalism, hiding his emotions behind a fixed expression and showing neither remorse nor pleasure in his mission. He also showed a strong impulse to kill Uri Reiss when they first met.
Kenny expressed a desire to live a "fun" life, but had a strange idea of what he considered "fun," commenting that he believed his grandfather's story about the Ackermann family's history because it would be more fun to do so, and commenting that growing old and living a full life did not sound fun. The only thing stranger than his idea of fun was his sense of humor, seen when he said that his grandfather's story about the persecution of the Ackermanns was "funny," and when he freed Eren Jaeger in order for him to fight against Historia just for his own entertainment, even though the future of humanity was at stake.
Even so, he was able to show true admiration and respect to those who he believed deserved it, like Uri or his second in command. He could also be seen at time displaying genuine care for others, killing MPs that came near his grandfather's home so that they would not harass him, and raising his nephew Levi following his sister's passing. This care for others could also be seen briefly in his interactions with Historia in the Reiss chapel, becoming noticeably saddened to see Historia's slavish devotion to her father's will, despite the consequences that she would face if she followed through with is plan to inherit the Founding Titan. Though this is not to say he was overly caring. He disliked cowards and did not respect them, and cared even less for titles, not hesitating to threaten Rod Reiss, the true king of the Walls.
Kenny later revealed that he only obeyed Rod as a plan to obtain power, and that his true intentions were always to become a Titan and gain the Founding Titan himself, which was in direct opposition with Rod's goals. After witnessing Uri and later Frieda Reiss become benevolent people after inheriting the Founding Titan, he wondered if the same thing would happen to him too. He wanted to know what does it feel like to be kind and compassionate. His grand dream was to take the Founding Titan and see the world like Uri once did.
Despite his outward confidence, Kenny seemed to suffer from some degree of self-loathing, going so far as to describe himself as "garbage," and his entire quest for power was motivated by his hope that gaining more power would make him a more compassionate person like Uri. His lack of self-confidence was also demonstrated by his decision to abandon Levi when the latter was still a child, reasoning that he was not meant to be someone's parent.
At some unspecified point, either before or after becoming a serial killer, Levi recalls Kenny saying he felt a sudden inexplicable surge of power and with it he knew "exactly what to do."
Kenny made a name for himself as a mass murderer, infamous for having managed to kill over 100 members of the Military Police Regiment.
One day, after having killed some MPs who were snooping around his grandfather's house, Kenny went to visit his grandfather. He informs his grandfather that he has learned of a branch of their family that is living in Shiganshina District, but notes that they are impoverished due to interference by the MPs in their area. Reminding his grandfather that their family used to serve the king, he demanded to know why they are now being treated the way that they are. His grandfather explained that the king fears their family, because they are immune to his power which allows him to alter the memories and control the people of the Walls, and control them and that they faced persecution because they, along with the Oriental clan, chose to turn their backs on the king's ideology.
Kenny also informed his grandfather that he had managed to find his sister, Kuchel, working in a brothel in the Underground. He was unhappy to learn that Kuchel had been impregnated by one of her clients and that she intended to keep the child, and sullenly mused that there was no dream worth living in the world that they did.
Sometime after that conversation, Kenny talked with a contact in the government, who informed him of the existence of the Reiss family, the true royal family within the Walls. Kenny tracked down Uri and Rod Reiss and tried to kill them, but failed when Uri partially transformed into a Titan and trapped him in his hand.
Though Rod tried to shoot Kenny while he was immobilized, Uri stopped him, wanting to interrogate him to discover the identity of his contact; finding Kenny's hatred towards them justified due to the persecution that the Ackermanns suffered at the hands of the monarchy.
Kenny attempted another attack by throwing his knife at Uri, though the latter stopped it with his arm. Seeing this, Kenny started screaming at Uri, asking for another chance to prepare a proper ambush. To Kenny's shock, Uri released him, and even bowed before him, apologizing for the persecution towards the Ackermanns and pleading him to spare his life. Kenny was surprised to see this coming from a king with that much power, and offered to help Uri, which the latter accepted.
Kenny became Uri's bodyguard and close friend, and remained at his side until the latter's death. After some years, he returned to the Underground to see Kuchel, but found that she had been dead for some time. He found, and then adopted, her son Levi but introduced himself to Levi as a close friend of Kuchel's, without revealing that he was Levi's uncle. Kenny lived with Levi and trained him, teaching the boy everything he knew about how to survive. Once he was reasonably sure that Levi would be able to survive on his own, Kenny abandoned the boy, feeling that he was unfit to be a parent.
Years later, Uri explained that he would not be long for the world, and he would be passing his powers to some of Rod's children, but that he would live on in their memories. Uri told him that he saw the world as ending in some time but before it happened, he wanted to make a paradise for mankind.
After Uri passed the Founding Titan to his niece Frieda and died as a result, Kenny made a plan to obtain the same Titan powers Uri had and used his influence to establish the Anti-Personnel Control Squad. On his first day as captain, Kenny introduces himself to his new subordinates, acknowledging himself to be the man who slaughtered many of their comrades when he was still a serial killer. However, one of the soldiers, Caven, speaks up, explaining that his past did not matter to them. She explained that they had given up on killing Titans, and the only remaining alternative to them was killing humans. Caven's words greatly pleased Kenny, and he began to single her out as his favorite soldier and second in command.
In the year 845, days after the fall of Wall Maria, Kenny arrives with a group of soldiers at Historia Reiss' home. He grabs Historia's mother and asks Rod Reiss if she and Historia are related to him. Rod Reiss denies it and Kenny slits Alma's throat. He approaches Historia to kill her too, but Rod Reiss orders him to stop and saves her life, giving her the new name "Christa Lenz" to live by.
The two watch as Military Police unsuccessfully attempt to raid the cottage and detain its occupants, with Kenny commenting that Levi was able to mobilize his subordinates fast enough to avoid capture because of his training.
Kenny follows Levi's squad to Trost District, where he employs the help of Dimo Reeves and the Reeves Company to kidnap Eren and Historia. Although the locals kidnap decoys, Kenny sees through the ruse and tracks down the real Eren and Historia. Seeing that Levi is keeping watch over the covered wagon that Eren and Historia are in from afar, Kenny flanks Levi and his companion Nifa in order to kill them. Although he is successful in killing Nifa, Levi anticipates Kenny's flanking maneuver and manages to survive his attack.
As Kenny's subordinates kill another of Levi's companions, Kenny jovially insults Levi's small stature as he reloads his guns and uses his ODM gear to get another clear shot. Levi manages to escape, dodging Kenny's gunshots as he flees. Kenny's squad pursues Levi, eventually forcing him to take shelter in a nearby tavern.
Kenny follows Levi into the tavern, but is not able to find him. Concluding that Levi is not there, he is caught off guard when Levi begins to talk to him from under the counter. Levi expresses amazement at Kenny's working with the Military Police, but Kenny brushes him off, claiming that he would not understand such adult matters. Kenny continues to taunt Levi, criticizing his decision to join the Scout Regiment and throwing chairs over the bar to antagonize him. As he tries to get closer to Levi, Levi shoots him with the tavern owner's gun. Kenny manages to block the bullet with a chair, saving his life, but is knocked out of the tavern by the force of the impact.
As Levi makes his escape, Caven comes to check on Kenny. Kenny notes Levi's growth since they last parted, and laments that his dream is slipping away from him. Having personally given up the pursuit of Levi, Kenny delivers Eren and Historia to Rod Reiss.
Learning that Reeves has double crossed the Military Police and sided with the Scout Regiment, Kenny tracks down Reeves and, under the cover of night, kills him. Caven is concerned that he did not attempt to find out Levi's location from Reeves, but Kenny assures her that Levi will eventually come to them. A day later, he would oversee members from the Scout Regiment being arrested while reminding Caven that Levi will show up on his own eventually.
In the cavern under the Reiss Chapel, Kenny listens on as Rod helps Historia unlock her memories of her sister Frieda, and Eren his memories of his father's last moments. As Historia absorbs the information, Kenny reveals himself, and informs Rod that the military has switched sides, overthrown the puppet king, and taken over with Dhalis Zachary in charge. He encourages them to hurry, as they are almost certainly being pursued. Rod orders Kenny to take his squad and guard the entrance to the chapel, as he can only move forward once the Anti-Personnel Control Squad leaves. Clearly displeased, Kenny tips his hat and departs. As he leaves, he recalls one of the last conversations he had with his grandfather.
Kenny arrives at the mouth of the cavern to find his squad engaged with Levi's, arriving just in time to save Caven from Levi. Like in their previous encounter, Kenny tries to flank Levi, but this time Levi is ready to counter him. Kenny begins firing at platforms stationed throughout the cavern, distracting Levi with the debris created in order to get in close and attack him with his knife. As Levi tries to get out of range Kenny fires at him again, but Levi uses a pouch of gasoline to block the blast, creating an explosion. Levi uses the cover provided by the explosion to get in close with his swords, and although Kenny is able to block the majority of Levi's strike with his knife, he is still dealt a sizable cut to his midsection. Kenny and his squad retreat farther into the cavern, with Kenny firing off one last shot at Levi as he flees.
Kenny returns just in time to hear Rod reveal to Historia that the Founding Titan's power can only be fully realized by a member of the Reiss family. He asks Rod to confirm what he just said about only a Reiss being able to obtain the Titan's power, which he does. Having planned to become a Titan himself and steal Eren's power, Kenny becomes visibly distraught as he realizes that his plan is pointless.
Growing angry, he lifts Rod into the air by the collar and begins to threaten him, upset that Rod knew his intentions and strung him along. Rod replies that he is grateful but also that he was unaware why his brother ever took "a dog like you" off the streets. Kenny interrupts him and says that if he insults Uri once more, he will blast Rod's face in half. Historia knocks Kenny's gun away, demanding that he let go of her father. Kenny reminds her that Rod is trying to turn her into a monster who will eat Eren, but Historia replies that she will do it if it is her mission, adding that there is nothing sad about saving humanity. Kenny reminds her what Rod did to her; that her birth was a tragedy and only conceived because Rod wanted to feel good with a servant. Kenny does not believe the notion that Rod saved Historia out of love and claims that he only did it because Grisha killed the rest of his children and he needed Historia's blood, which is why the Order of the Walls had been keeping an eye on her.
Kenny begins shoving a knife down Rod's throat as he claims that Rod did not want to turn himself into a Titan and so used his family. Kenny claims that Rod covered up the theft of the Founding Titan's power in order to keep the Reiss family in power, and did not start talking until after Eren saved Trost District, which was only after innumerable sacrifices. Kenny concludes that Rod only cares about protecting himself and not his family, humanity, and especially not Historia. To Kenny's surprise, Rod is able to pull the knife out of his throat and tells Historia that Kenny is wrong. He admits that he has not told Historia some things but does reveal that he can not become a Titan himself for an unspecified reason.
Kenny releases Rod, and Rod tells him that he is free to leave and should go live a long life. Kenny sullenly remarks that Rod's suggestion would not be very fun, before ascending the stairs towards Eren, telling him to turn into a Titan, to the horror of the two Reisses. Kenny says that both Historia and Eren can become Titans and fight to the death, with peace returning if Historia wins and nothing changing if Eren wins. He slices Eren's forehead to help him transform, and asks Rod if he can truly call dying of natural causes living.
Kenny uses his ODM gear to pull himself up to a safe distance while remarking to himself that he should get away from what is about to happen. However, Kenny gets very surprised when Historia hesitates to inject the serum. He even starts laughing after Historia rejects the serum, harms her father and tries to release Eren, cheering the two for making things far more interesting. However, when Rod transforms himself into a Titan, Kenny gets dragged by Rod's heat and sheer size, cursing Rod for becoming a Titan. As Kenny tries to escape using his ODM gear, he sees his squad coming towards him. He tries to warn them to stay away, but is only able to watch as they are crushed under the falling debris.
While his squad is crushed in the falling debris from the cavern, Kenny manages to survive and escape. However, he is heavily injured in the process, receiving severe burns all over his body from Rod's transformation. As he exits the remains of the cavern, Kenny slowly makes his way to a nearby tree, where he takes off his armor and collapses. As he rests, he recalls the day that he abandoned Levi as a child, but his reminiscing is interrupted by the arrival of Levi himself. Levi observes that Kenny's injuries have left him on the verge of death, and Kenny responds by smugly revealing that he has a Titan injection, which could allow him to save himself.
Levi is confused as to why Kenny has not already used it to save his own life. Kenny claims that he was afraid of ending up like Rod, but Levi is not convinced and asks if he has a better explanation. As Kenny tries to think of one, he recalls all of the important people of his past, and comes to the realization that they all had something that drove them, which he has lost. At the brink of death, Kenny confesses that he is Levi's uncle, explaining that he left Levi because Kenny viewed himself not fit to be a father. As a final gift, Kenny gives Levi the Titan injection that he stole from Rod. Soon after, he dies, sitting under the tree where he rested.
- Levi Ackermann - Kenny trained Levi when they were younger, and they even lived together. He appeared to have some respect for Levi since he called him "his pride" and though he respected Levi, his dream appeared to be killing him. The meaning behind their similar last names implies a familiar relationship, however Levi was unaware of his last name until he was told by a soldier, though he was not surprised by him being an Ackermann.
- Rod Reiss - Though initially Kenny seemed to be loyal to Rod, being a sort of "right-hand man" for him, it was later revealed that he does not like him at all, believing that he is a coward that only cares about himself, and only obeyed him because he wanted to steal the Founding Titan from him. When Rod revealed that the Founding Titan would be useless if it were not used by a member of the Reiss bloodline, Kenny showed his true colors and did not hesitate to insult and threaten Rod.
- Historia Reiss - Kenny killed her mother, Alma, without hesitation and was going to kill Historia had Rod not intervened. Years later, he insulted her when he captured her and Eren, saying that in the five years since he last saw her, she has barely grown. However, he appeared to pity her, as he tried to tell her that Rod was going to make her turn into a Titan and eat Eren and told her that Rod was a liar and a coward.
- Caven - Kenny held great trust in all his soldiers, but he was especially impressed by Caven's professionalism and unwavering loyalty. He eventually saw much promise in her and designated her as his second in command.
- Hajime Isayama has stated that Kenny's character was partially inspired by the character Trevor Philips from Grand Theft Auto V.