Levi
Ackermann

Levi grew up in the underground city beneath the capital, the son of a prostitute named Kuchel who died while he was still small. The man who found him half-starved beside her body was Kenny the Ripper, who fed him, taught him the knife and how to survive, and walked out one day without ever telling the boy he was his uncle. Levi came up from that hole a thug with an Ackermann's impossible strength, and it was Erwin Smith who pulled him into the Scout Regiment, where people took to calling him humanity's strongest soldier.

He built the Special Operations Squad out of soldiers he trusted, and the Female Titan killed all four of them in the space of minutes. Levi's answer to loss never changed: no one can know the outcome in advance, so make the choice you will regret least, a lesson he hammered into Eren after forcing exactly that choice on him in the forest. He carved the Female Titan apart to take Eren back, faster than she could harden, and put down his own uncle's Anti-Personnel Squad in the caverns under the Reiss chapel. Kenny, dying, finally told him whose brother he was and left the Titan serum in his hands.

That syringe became the worst decision of his life. On a rooftop in Shiganshina, with Erwin gutted by the Beast Titan's barrage and Armin burned into a husk, Levi chose to let Erwin rest instead of dragging him back to the nightmare, and gave Armin the injection. He had already promised Erwin the Beast Titan's head in exchange for sending him to die, and he nearly collected it that same day, shredding the Beast in seconds and tearing Zeke out of its nape before the Cart Titan snatched him away.

The promise took years and most of his body to keep. Zeke's scream turned Levi's own escort into Titans, and Levi killed every one of them, former comrades included, to reach him. Zeke detonated a Thunder Spear against his own stomach rather than stay caught, and the blast took fingers from Levi's hand and nearly his life. He spent the Rumbling being hauled on a litter, held together by stitches, and still stood at the final battle, where he took Zeke's head off in a single stroke and stopped the walking Wall Titans cold. He survived the end of the Titans, the vow to Erwin finally paid.