Captain Kenny Ackerman is a character from Attack On Titan and an antagonist of the series and uncle to Levi Ackerman and brother of Kuchel Ackerman.
He was an infamous serial killer that stalked people in the capital of the kingdom, Mitras. His most known way to kill was to slit the throats of his victims which earned him his infamous handle "Throat Slasher Kenny", and it was rumored that he murdered over 100 members of the Military Police Brigade. He also trained Levi when he was younger and later they parted ways. Kenny became a member of the 1st Brigade. He raised Levi as own after his sister Kuchiel who is protsutie
Many years later, after the breaking of Wall Maria he killed a prostitute, the mother of Historia Reiss after asking to Rod Reiss if her and Historia were related to him. Lod Reiss denied it and Captain Ackerman slit Historia's mother's throat. He wanted to do the same with Historia but her father Rod Reiss saved her life by telling her that her new name would be Christa Renz, and she was never allowed to talk about what happened in that farm.
Years later Captain Ackerman appears as the leader of group sent to retrieve Eren and Historia from Dimo Reeves. He tells Reeves that he personally trained Levi and then kills him in the same way he killed Historia's mother, claiming that it is his own fault for Reeves' betrayal.
After the death of Dimo Reeves he kidnaps Eren and Historia and later, along with his men, he kills Nifa, Keiji and the guy with the goggles.