Born in Shiganshina District within Wall Maria to parents Grisha and Carla Yeager, Eren Yeager's childhood was marked by a fascination with the world beyond the walls, ignited by Armin Arlert's book depicting oceans and fiery waters. This yearning for freedom clashed with his father's medical focus and his mother's protective instincts, coexisting alongside a growing hatred for the Titans who confined humanity. A pivotal trauma struck in 845 during Wall Maria's fall: trapped helplessly under debris, Eren witnessed the Smiling Titan kill his mother, cementing his vow to exterminate all Titans. Shortly after, his father injected him with a Titan serum, granting transformative abilities, and entrusted him with a key to the family basement, instructing him to reclaim Wall Maria and uncover the truths hidden there. Eren joined the 104th Training Corps in 847 alongside adoptive sister Mikasa Ackerman and friend Armin Arlert. He graduated fifth in his class, demonstrating significant combat initiative and close-quarters proficiency, though he struggled with teamwork and tactical judgment. His intense determination often manifested as reckless bravery. During the Battle of Trost District, a near-fatal experience triggered his first uncontrolled transformation into a 15-meter Titan, revealing his ability to become the very creature he despised. Activating this power required self-harm and focused purpose, granting immense strength, endurance, and regeneration, saving his life repeatedly. However, it also led to military suspicion, temporary imprisonment, and intense scrutiny under Captain Levi's squad in the Survey Corps. Confrontations like the Female Titan's attack in the Forest of Giant Trees and Stohess District forced Eren to face his limitations and emotional volatility. He struggled to control his Titan form in combat, particularly against Annie Leonhart, fueled by rage and betrayal. Later, the Clash of the Titans arc brought profound disillusionment when he learned comrades Reiner Braun and Bertholdt Hoover were the Armored and Colossal Titans responsible for his mother's death and Wall Maria's fall, shattering his simplistic worldview. Events at Utgard Castle and the escalating Titan threat within Wall Rose exposed him to deeper Titan mysteries, including Titans embedded within the Walls themselves. Interactions with Commander Erwin Smith and Section Commander Hange Zoë during missions shaped his understanding of strategy and survival's cost. Reaching the Yeager family basement in Shiganshina proved transformative. Grisha's journals and memories unveiled the true history of Eldia and Marley, the origin of Titans from Ymir Fritz, the nature of the Nine Titans, and the reality that humanity thrived beyond the Walls, viewing Paradis Island Eldians as devils. Eren learned he inherited both the Attack Titan and the Founding Titan from his father, who obtained the latter by force from the Reiss family. This knowledge reframed his existence: Titans were human-created weapons, and the true enemy lay across the ocean. His goal shifted from Titan extermination to securing Paradis's freedom from global persecution. This culminated in the 854 Raid on Liberio, where he consumed Lara Tybur, gaining the War Hammer Titan's power. Infiltrating Marley under the alias "Eren Kruger," he manipulated events to initiate conflict, declaring war and activating the Rumbling. Contact with Ymir Fritz in the Paths dimension allowed Eren to access the Founding Titan's full power. He initiated the near-total annihilation of the world beyond Paradis using the Wall Titans. His Founding Titan manifested as an enormous, skeletal structure towering over Colossal Titans, moving on elongated ribs. This genocidal act stemmed from his belief it was the only way to end the cycle of hatred and ensure his friends' long-term safety, coupled with his innate childhood drive for personal freedom. Executing the Rumbling exacted a severe psychological toll, leading him to deliberately alienate Mikasa and Armin to position them as heroes who could stop him. Internally conflicted and overwhelmed, he confessed fear, regret, and a childish desire for Mikasa's devotion in his Paths conversation with Armin. His complex feelings for Mikasa intertwined with deep-seated insecurities about his strength and perceived inability to protect her, rooted in his mother's words and societal expectations. Mikasa ended his life to halt the Rumbling, severing the Titan curse and reverting all Titans to humans. Eren's physical appearance evolved. As a child and young cadet, he had short black/dark brown hair, teal-green/gray eyes, and an average, later muscular build. Post-timeskip by 854, he grew taller with shoulder-length hair often tied back, a slight mustache and goatee, and bandages covering his forehead and left eye. During his Marley infiltration, he wore an Eldian armband. Later, he adopted a simple black mantle over a white shirt and dark pants. His Attack Titan form consistently featured a 15-meter muscular frame, elongated features, exposed teeth, and deep-set eyes. His Founding Titan form presented a colossal, grotesque skeletal structure with a fleshy head suspended within a massive ribcage. Personality-wise, he retained core traits of intense determination, protectiveness towards loved ones, and impulsiveness. His experiences, particularly learning the world's truths and seeing the future through the Attack Titan's power, fostered a more calculated and detached exterior later in life, masking profound emotional turmoil, guilt, and fatalistic resolve. His worldview evolved from simplistic black-and-white morality focused solely on Titan extermination to a complex, albeit extreme, understanding of cyclical violence and perceived necessity.