Keith Shadis headed the 104th Training Corps, molding cadets into soldiers. He previously commanded the Survey Corps as its 12th leader, the sole commander to resign before death, stepping down in 845 after repeated disastrous expeditions and massive losses under his watch. His predecessor was the 11th Commander; Erwin Smith succeeded him. In his youth, Keith dreamed of the world beyond the Walls and joined the Survey Corps, developing a self-righteous personality and seeing himself as "different." This conviction deepened after meeting Grisha Yeager outside Wall Maria in 832. Grisha hailed Keith and the Corps as "chosen ones," cementing Keith's belief in his own special destiny. He grew dismissive of others and resistant to new strategies, like Erwin Smith's "Long-Range Scouting Formation," trusting only his own plans. His command yielded no progress, only heavy casualties and public contempt. Keith held unrequited feelings for Carla, a Shiganshina barmaid. He introduced Grisha to her during an epidemic; Grisha cured her, but Keith was wounded when they later married. After a failed expedition, Carla confronted him with her infant son Eren, voicing fears for his safety. Keith angrily dismissed her as "ordinary" and incapable of grasping greatness. He deeply regretted these words after Carla died in Wall Maria's fall. His resignation came after a final failed mission where he confessed to a fallen soldier's mother that his expeditions achieved nothing. Shattered by realizing he was not "special," he named Erwin his successor. That same night, he helped Grisha search for Carla after Wall Maria's breach, finding only Eren unconscious in the woods after Grisha vanished. Keith brought Eren to safety. As the 104th's instructor, Keith adopted a harsh, intimidating persona to enforce discipline. He deliberately tampered with Eren's vertical maneuvering gear during training, hoping to force him out of the military and spare him. Witnessing Eren's fierce determination during a retest, Keith relented, feigning discovery of the faulty gear and permitting Eren to continue. Years later, during the Yeagerist uprising, Keith was denounced as an "archaic relic" and ousted. Former cadets publicly beat him to prove loyalty to Eren. Inspired by their resolve to stop the Rumbling, he destroyed a Yeagerist supply train to aid their escape. He then partnered with Marleyan commander Theo Magath to rig a boat with explosives. As Yeagerists closed in, they detonated it, sacrificing themselves to delay the pursuit. Magath declared Keith would be remembered as a savior, but Keith dismissed this, consistent with his lifelong view of himself as a "bystander."