Eren Yeager entered the world on March 30th within Shiganshina District, born to Grisha and Carla Yeager. Childhood curiosity about the world beyond the Walls, ignited by Armin Arlert's book revealing oceans and wonders, rapidly transformed into contempt for those accepting confinement as "livestock." His resolve manifested violently when he hunted down and executed two men who kidnapped Mikasa Ackerman, branding them "animals" undeserving of life. Mikasa subsequently joined the Yeager household as their adopted daughter. The year 845 brought catastrophe. The Colossal Titan shattered Wall Maria, flooding Shiganshina with Titans. Eren watched helplessly as the Smiling Titan devoured his mother; Hannes rescued Eren, Mikasa, and Armin. This horror cemented Eren's hatred for Titans and his oath to exterminate them. Shortly after, Grisha injected Eren with a Titan serum, entrusted him with a basement key, and commanded him to reclaim Wall Maria before vanishing, leaving Eren with only fragmented memories. Eren, Mikasa, and Armin enlisted in the 104th Training Corps in 847. Upon graduation, Eren ranked 5th, his fierce determination evident though hampered by struggles with teamwork and tactical thought. His volatile temper and impulsiveness often sparked conflict, yet his resolve garnered respect. He immediately joined the Survey Corps. During the Battle of Trost in 850, Eren sacrificed himself to save Armin from a Pure Titan, only to later emerge encased within his newly revealed Attack Titan form – a 15-meter-tall entity defined by a muscular build, elongated features, exposed teeth, and limited speech. This transformation sparked military suspicion, nearly leading to execution until Armin intervened. Eren later deployed this Titan form to seal Wall Maria's breach, cementing his status as "humanity's weapon." Subsequent events fractured Eren's worldview. He battled the Female Titan, revealed as comrade Annie Leonhart, and later discovered Reiner Braun and Bertholdt Hoover were the Armored and Colossal Titans responsible for his mother's death. During the clash with Reiner, Hannes perished shielding Eren and Mikasa from the Smiling Titan. Consumed by rage, Eren activated the Founding Titan's power, commanding nearby Titans to consume the Smiling Titan. Captured by the Reiss family, Eren confronted further truths: his father murdered the Reiss family to steal the Founding Titan, transferring it to Eren. Historia Reiss's royal lineage and Rod Reiss's manipulations forced Eren to question his father's motives and his own worthiness. Unlocking Grisha's memories via the basement key revealed Eldia's history, Marley's oppression, and the world beyond Paradis Island. This shattered Eren's belief in Titans as the sole enemy, redirecting his fury toward Marley and the global persecution of Eldians. By 854, Eren infiltrated Marley undercover, sporting longer hair, facial hair, and bandages over his left eye. He instigated the attack on Liberio, assassinated Willy Tybur, and consumed Lara Tybur to seize the War Hammer Titan. This marked his evolution into a strategic, morally ambiguous figure. He severed ties with Mikasa and Armin, feigning disdain to protect them, and manipulated Floch Forster to forge the Yeagerist faction. His actions culminated in initiating the Rumbling – unleashing the Wall Titans to annihilate the world beyond Paradis. As the Founding Titan, Eren's form evolved into a colossal skeletal structure, dubbed the "Doomsday Titan" or "End Titan," featuring a kilometers-spanning ribcape and an undersized upper body suspended by sinew. This form executed the Rumbling's global devastation. Internally, Eren confessed conflicting motivations: a yearning for absolute freedom warring with love for his friends, particularly Mikasa. He admitted engineering his own death at their hands to make them global heroes, securing Paradis's temporary safety. His final act shared an alternate reality vision with Mikasa, depicting four years of peaceful coexistence.