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|No matter the age, this Titan has always moved ahead, seeking freedom. It has fought on for freedom.|
|— Eren Kruger describes his Titan|
The Attack Titan (進撃の巨人 Shingeki no Kyojin?, also translated as Attacking Titan) is one of the Nine Titans that has fought for Eldia throughout the generations. It is currently in the possession of Eren Yeager.
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 the island of Paradis where King Karl Fritz relocated the capital.
In the year 819, an Eldian spy in the Marley Public Security Authorities 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 Yeager to the island of Paradis. At the borderline, after the Eldia Restorationists were turned into mindless Titans and sent to wander the island, Kruger made use of the Attack Titan to destroy the Public Security Authorities and their ship before disposing of all evidence of the event. Afterwards, Kruger entrusted Grisha with his 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 Shadis of the Survey Corps. After his arrival in Shiganshina District, it is unknown how often Grisha made use of his Attack Titan.
After holding the Attack Titan for thirteen years, Wall Maria came under attack by the warriors of Marley, and Grisha decided the time had come to negotiate with the Founding Titan or take it by force. Arriving at the Reiss Chapel, Grisha pleaded with Frieda Reiss for the sake of Eldia and the Walls, but his cries were neglected. Left with no choice, Grisha used the Attack Titan against Frieda's Founding Titan and overpowered her, stealing her Founding Titan and killing her along with the rest of her family excluding her father, who escaped.
Upon returning to Wall Rose where the refugees from Wall Maria were arriving, Grisha found his son Eren Yeager and took him into a forest where he injected him with a Titan serum. As a mindless Titan, Eren ate his father and inherited both the Attack Titan and the Founding Titan, though he could not use the latter due to his non-royal lineage.
For five years, Eren Yeager lived his life unaware of his possession of the Attack Titan and the unusable Founding Titan until the year 850, during the battle of Trost District. Upon being caught and eaten by a Titan, Eren's injuries and burning desire to slaughter the Titans trigger his first transformation into the Attack Titan. In a nearly mindless state, Eren wanders Trost as the Attack Titan, slaughtering twenty Titans throughout the day all while avoiding bringing harm to the human trainees around him. His first Attack Titan eventually exhausts itself, and Eren emerges with healed wounds.
Completely clueless as to the nature of Eren's Titan power, 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 the Attack Titan and protects himself and his friends from the blast. Upon Commander Dot Pixis' arrival in Trost, the military decides to make use of the Attack 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 Attack Titan falls into a feral state and attacks Mikasa Ackerman before incapacitating itself. Eren's Titan lies dormant for a short time before his friend Armin Arlert manages to communicate with Eren himself through the nape of the Attack Titan, and Eren regains control. Carrying a massive boulder through the streets as members of the Garrison and Training Corps defend him, the Attack Titan seals the hole in the Wall, securing humanity's first victory against the Titans.
Some time afterwards, Eren joins the Survey Corps after his change of custody is made official in a military tribunal. During his first month in the Survey Corps, Eren's Attack Titan is subjected to a variety of studies by Squad Leader Hange Zoë. At this time, the Survey Corps 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 Survey Corps sets out on the 57th Expedition Outside the Walls. However, the expedition is sabotaged by the arrival of the Female Titan. Within a Titan Forest, Eren's Attack Titan battles the Female Titan, but he is defeated. While Eren is later rescued from the Female, the expedition is cut short and is considered a failure.
A few days later, the Survey Corps corners Annie Leonhart, holder of the Female Titan, in Stohess District, and she transforms into the Female Titan once more as a last resort. Eren battles her a second time with the Attack Titan, though the raid comes to an end when Annie uses her hardening ability to encase herself in a crystal-like substance to avoid capture.
The next day, Eren joins the Survey Corps' efforts in dealing with the sudden Wall Rose invasion. At this time, Reiner Braun and Bertolt Hoover reveal their respective identities as the Armored Titan and Colossus Titan. When the two transform into their Titan forms, Eren battles the Armored Titan with the Attack Titan. Despite initial difficulties, Eren's Titan gains the upper hand and nearly defeats the Armored Titan until Bertolt's Colossus Titan cuts the battle short in a last-resort effort to capture Eren. In the subsequent mission to rescue Eren, the Attack Titan is not used, but instead Eren manages to unlock the power of the Founding Titan for a brief moment after making contact with a Titan of royal blood.
During the week after the invasion, the Survey Corps goes into hiding as Military Police Brigade action against them increases disturbingly. Research on Eren's Attack Titan continues in the wilderness, where they observe that repetitive transformations in a short amount of time lead to decreased physical and mental strength in the Attack Titan. Some time later, Eren is captured by the Reiss family, who desire to feed Eren to Historia Reiss in order to regain the Founding Titan for the royal family. While captured, Eren witnesses his father's memories of using the Attack Titan against the royal family as well as the moment where he ate his father to gain his Titan. During his rescue, Eren ingests a Titan serum labelled "armor", and the Attack Titan gains the ability to harden its skin in a manner similar to the Wall Titans and Annie's Female Titan. This armor ability is used to protect Eren's friends from the collapse of the cavern beneath the Reiss Chapel, and Eren uses his Titan to toss a bundle of explosives into the gargantuan Titan form of Rod Reiss.
After Rod Reiss' defeat and the crowning of Historia Reiss, Eren's hardening power is used to create a Titan guillotine where the southern gate of Trost District once stood. The new anti-Titan weapon is a success, though it takes a heavy toll on Eren's health for a brief time after emerging from his Titan. Shortly afterwards, the Survey Corps sets out for the ruins of Shiganshina District in order to reclaim the lost territory of Wall Maria. Eren's Attack Titan uses its new hardening power to completely seal breach in the southern gate of Shiganshina, but 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.
Before Reiner can be killed, Bertolt comes to his rescue and wards off the recruits of the Survey Corps before transforming into the Colossus Titan. Eren attempts to attack the Colossus, but he is kicked into Wall Maria and is briefly incapacitated. Armin once again brings Eren back to his senses, and he formulates a plan for Eren to defeat the Colossus. As Armin distracts Bertolt, Eren's Attack Titan falls to the ground near the breached north gate of Shiganshina and hardens itself. Thinking that Eren has succumbed to a concussion, Bertolt thinks nothing of it but soon realizes that he is seeing the hardened shell of a Titan and not Eren's true Titan, and in the moment of vulnerability Eren in human form strikes at the nape of the Colossus Titan, pulling Bertolt out of his defeated Titan form.
In the aftermath of the battle for Shiganshina, the survivors of the battle arrive at the basement of the Yeager family's home, where Grisha Yeager had left three books which, in addition to information of the outside world, detailed his past as well as the moment when he inherited the Attack Titan from Eren Kruger nearly twenty years ago.
Through the years 851 to 854, the nation of Marley sent a total of 32 scouting ships to the island of Paradis, all of which ended up missing. While the details concerning their disappearances are currently unknown, Zeke Yeager theorizes that at least two Titans, including Eren, are responsible for destroying all the investigation ships.