Eren Jaeger was born on March 30, 835, within Shiganshina District of Wall Maria to Grisha and Carla Jaeger. His childhood burned with a fierce desire for freedom and deep resentment toward the walls confining humanity, fueled by his friend Armin Arlert's book depicting the outside world. This intense curiosity led him to scorn those content with life within the walls as "livestock". At age nine, Eren encountered Mikasa Ackerman after human traffickers murdered her parents. Defying his father's instructions to stay behind, he tracked the kidnappers, killing two to rescue her, demonstrating early traits of extreme protectiveness and violent resolve. The Jaegers adopted Mikasa, integrating her into their family. In 845, the Colossal Titan breached Wall Maria, leading to Shiganshina's invasion. A boulder crushed the Jaeger home during the attack, trapping Carla. As Eren and Mikasa tried to free her, the Smiling Titan approached. Garrison soldier Hannes rescued the children but failed to confront the Titan, leaving Carla to be devoured as Eren witnessed in horror. This event ignited his all-consuming hatred for Titans and his vow to eradicate them. Following the retreat to Wall Rose, Grisha injected Eren with an unexplained serum and entrusted him with a basement key, instructing him to reclaim Shiganshina. Grisha then disappeared, leaving Eren with fragmented memories. Amid widespread famine, Eren condemned the government's failed expedition to retake Wall Maria, which sacrificed 250,000 refugees. In 847, he enlisted in the military alongside Mikasa and Armin. During training with the 104th Cadet Corps, Eren initially struggled with omni-directional mobility gear due to defective equipment but excelled after a retest. He ranked fifth at graduation, behind Mikasa (first), Reiner Braun, Bertholdt Hoover, and Annie Leonhart. His rivalry with Jean Kirschtein intensified over opposing ideals: Jean sought safety in the Military Police, while Eren viewed such complacency as cowardice. Eren, Mikasa, and Armin chose the high-mortality Survey Corps. During the 850 Trost District attack, the Colossal Titan reappeared, causing mass casualties. Eren lost his left leg saving Armin from a Bearded Titan and was swallowed. An unidentified Titan emerged shortly after, attacking other Titans. Mikasa observed this Titan protecting humans, and upon its defeat, Eren emerged unscathed from its nape. Military authorities imprisoned him as a potential threat, but Armin argued Eren could seal Wall Rose's breach. Eren later lifted a boulder while in Titan form, enabling the mission's success. Physically, Eren possessed a lean, muscular build, short dark brown hair, and teal eyes (gray in some sources). He wore standard Survey Corps attire and kept his father's key on a necklace. His Attack Titan form stood 15 meters tall, featuring elongated ears, a lipless mouth exposing teeth, a hooked nose, and a well-proportioned muscular frame. Transformation required self-injury and a focused objective, though emotional turmoil could hinder the process. Personality-wise, Eren embodied relentless determination, impulsiveness, and a binary worldview. He exhibited fierce loyalty to friends and family but struggled with empathy and self-doubt, often blaming himself for failures. His rage against oppression manifested in extreme violence, yet he valued human curiosity and sacrifice. These traits fueled his actions but also led to reckless decisions, like confronting superiors or charging into battles unprepared.