Born on March 30, 835, in Shiganshina District to Grisha and Carla Yeager, Eren Yeager developed an intense yearning for freedom beyond the Walls after seeing Armin Arlert's book depicting the outside world. This worldview fueled conflicts with peers and authority figures content within the Walls. At age nine, accompanying his father to the Ackerman residence, Eren killed human traffickers to rescue Mikasa Ackerman without remorse, revealing early violent tendencies. His family subsequently adopted Mikasa. The year 845 brought pivotal trauma when the Colossal and Armored Titans breached Wall Maria. Eren witnessed his mother's death by a Smiling Titan as Hannes rescued him and Mikasa instead of fighting. This event cemented his hatred of Titans and thirst for vengeance. Soon after, Grisha injected him with a Titan serum in a forest, transforming Eren into a Pure Titan who consumed his father, inheriting the Attack and Founding Titans. Grisha also entrusted him with a basement key, instructing him to reclaim Wall Maria. In 847, Eren enlisted in the 104th Training Corps alongside Mikasa and Armin. Initially struggling with equipment and combat, he ranked 5th upon graduation in 850. His defining traits—impulsiveness, a fierce sense of justice, protectiveness towards friends, and a volatile temper—frequently led to reckless actions. During the Battle of Trost, he was swallowed by a Titan while saving Armin, triggering his first transformation into the 15-meter Attack Titan. This revealed his Titan-shifting ability, resulting in military suspicion and transfer to the Survey Corps under Levi Ackerman's supervision. Subsequent events reshaped his worldview: The Female Titan incident exposed Annie Leonhart; the Clash of Titans arc revealed Reiner Braun and Bertholdt Hoover as the Armored and Colossal Titans; the Royal Government arc uncovered his father's past and the truth of Paradis Island's history. These revelations shattered his black-and-white morality, showing Titans as oppressed humans and Paradis residents as subjects of external hatred. He later inherited the War Hammer Titan by consuming Lara Tybur during the 854 raid on Liberio. Post-timeskip, Eren's appearance changed significantly, featuring shoulder-length hair, a beard, and bandages covering injuries. His demeanor grew detached and strategic. After accessing the Founding Titan's full power through contact with Historia Reiss, he perceived past and future memories simultaneously, learning of global forces planning Paradis's annihilation. This deterministic perspective drove him to initiate the Rumbling—activating Wall Titans to destroy all life beyond Paradis—believing it would secure his friends' long-term freedom. He manipulated events, like the Liberio attack, to unite enemies against him, intending for Mikasa, Armin, and allies to stop him and become global heroes. His Founding Titan form during the Rumbling manifested as an enormous skeletal structure with elongated ribs functioning as legs and a partially fleshed head suspended from vertebrae. Internally, his decapitated head reconnected via Ymir Fritz's power. Throughout the campaign, he expressed conflicted motives: deep loyalty to Paradis and childhood friends versus acknowledgment of his horrific actions as unavoidable. His final act confirmed the self-villainization aimed at redirecting global hatred onto himself, enabling his friends to end the Titan curse and negotiate peace.