Tom Ksaver

In his human years Ksaver is recognizable by his round face, cropped dark hair, and the spectacles that Zeke Yeager later adopts as his own. His clothing marks his standing in Marley: the customary Warrior attire paired with the red armband identifying an Eldian granted honorary Marleyan status.

His Beast Titan borrows from a bighorn ram. Dark horns curve back from the skull, the muzzle stretches long around an animal's nose, and pale fur covers the head, neck, and upper torso. Like nearly every Titan it moves upright on two legs.

Curiosity defines Ksaver far more than any warrior instinct. The question of how the Titans came to exist fascinates him, and by his own admission that curiosity is what drew him into the Titan Biology Research Society. Around others he stays relaxed and quick to smile, an unhurried man who considers the Warrior ideal of trading away one's lifespan to invade foreign nations frankly stupid.

That warmth conceals a ruined interior. Ksaver blames himself for the deaths of his wife and son and quietly wishes to die as atonement, and his gentleness toward Zeke, whom he comforts after the boy denounces his own parents, is inseparable from that grief.

Ksaver spends his early adulthood in the Liberio internment zone, enduring the same Marleyan prejudice as his neighbors; in 817 he crosses paths with the young Grisha and Faye Yeager as an airship passes overhead. He later falls for a Marleyan woman and hides his armband from her, since marriage between their peoples is forbidden. The two wed and raise a son, but years on she uncovers his ancestry and, in shame, kills the boy and then herself. Shattered, Ksaver enlists as a Warrior intending it as a slow suicide, proves worthy of the Beast Titan by 829, and doubles as a researcher of the Titan powers, rarely using a Titan form he judges useless in war.

Partway through his tenure he begins watching the next crop of candidates and fixates on a struggling boy named Zeke Yeager, whom instructor Theo Magath dismisses. The two meet over a solitary game of catch, and their games become the foundation of a deep bond. When Zeke's parents turn out to be leading figures among the Eldian Restorationists, it is Ksaver who urges the boy to report them first and save himself, standing beside him as Grisha Yeager and Dina Fritz are taken away.

His research eventually yields a discovery he shares only with Zeke: beyond rewriting memories, the Founding Titan can alter the very bodies of the Subjects of Ymir. Zeke reasons that such power could sterilize their people and erase the Titan curse within a century, and Ksaver, confessing his family's fate and his regret at ever being born, embraces the idea. He later reveals a second secret, that the First King's vow renouncing war can be circumvented if a royal-blooded Titan cooperates with whoever holds the Founder. In 842, chained beneath an underground altar, he is fed to Zeke's mindless Titan, silently promising as he dies to always watch over his surrogate son.

Ksaver's shadow stretches across the war's finale. Zeke screams his name before detonating a Thunder Spear in the Titan Forest, and when Ymir Fritz raises the past inheritors to defend Eren Yeager during the Rumbling, Zeke reawakens Ksaver among them. Reclaiming his Titan, he helps hold back Eren's defenders and joins the other inheritors in lifting Armin Arlert skyward for the transformation that destroys the Founding Titan.