Eren Jaeger grew up in Shiganshina District, a settlement sheltered behind Wall Maria. His childhood fascination with the outside world, ignited by a book from his friend Armin Arlelt, conflicted with his mother Carla’s wish for his safety within the walls. Grisha, his secretive physician father, encouraged Eren’s ambitions and eventually injected him with Titan serum during Shiganshina’s fall, transferring the Attack Titan and Founding Titan powers. The Colossal Titan’s breach of Wall Maria and his mother’s death at the jaws of the Smiling Titan became pivotal traumas, fueling his vengeful hatred of Titans and fixation on their annihilation. These events also unraveled Grisha’s cryptic legacy—the basement key and serum—which shaped Eren’s future pursuits. Joining the 104th Cadet Corps, Eren trained with adoptive sister Mikasa Ackermann and Armin, ranking fifth in his class. His relentless determination and binary morality sparked clashes with peers like Jean Kirschtein, though his impassioned rhetoric sometimes rallied others to the Scout Regiment’s cause. At the Battle of Trost District, Eren’s latent Titan powers surfaced after a Titan swallowed him during Armin’s rescue. This marked his first deliberate use of the ability to shield allies, though military authorities initially doubted his control. His Titan’s hardening capability later proved vital in sealing Wall Rose’s breach. Discovering Grisha’s basement revelations—the Titan origins as transformed humans and the Eldia-Marley conflict—shifted Eren’s focus from Titan eradication to confronting external human foes. Infiltrating Marley as a soldier exposed him to enemy perspectives, fostering reluctant empathy for Warriors like Reiner Braun even as he steeled his resolve to defend Paradis. Securing the War Hammer Titan during the Liberio raid amplified his powers but demanded civilian casualties. Later, his activation of the Rumbling—unleashing Wall Titans to crush global opposition—signaled a stark departure from earlier idealism, positioning him as a morally conflicted strategist prioritizing Eldia’s survival at any cost. Physical transformations mirrored his ideological shifts: his Titan evolved from a 15-meter Attack Titan with raw musculature to a skeletal Founding Titan wielding apocalyptic force. As a human, he adopted longer hair and stubble during covert missions, his appearance growing increasingly gaunt under the weight of his choices. Relationships with Mikasa and Armin frayed under ideological divides, while his alliance with half-brother Zeke Jaeger—Beast Titan inheritor—balanced shared heritage against clashing plans for Eldia’s fate. These ties highlighted cycles of inherited conflict and vengeance. Eren’s final acts etched a paradoxical legacy: a freedom-driven revolutionary who unleashed catastrophic violence, guided by personal rage, protective fervor, and the Attack Titan’s memory-shaped fatalism.