Here I go with another proposal on a questionable (and detestable) candidate. Will it succeed? Probably not. But it doesn't hurt to try and get loose ends out of the way:
Ed, Edd n'Eddy is a relatively lighthearted comedy cartoon about the wacky adventures of a trio of friend their attempts to con their fellow neighbors in a cul da sac.
The series eventually came to a close with a big movie that tied up all the plots such as....
Who is he? What has he done?
Eddy's Brother (some say his name is Matt) initially presented as a cool big bro turns out to be a domestic abuser. When Eddy comes to his door looking for help, he acts nice at furst then insists they play Uncle for old time sake. He twists his leg amd laughs his ass off when Eddy gets hurt.
He repeatdly slams Eddy against his trailer. When Eddy tells him enough he just smugly asks him "Don't you want to hang with your hero?"
When Edd confronts him, Eddy's Brother just puts on a Slasher Smile (like a serial killer) and proclaims that he's been beating Eddy this same way his whole childhood, before using Eddy as a club to slam Edd into the ground.
Eddy's Brother keeps beating on Eddy and Edd. He is defeated when Ed uses a broken nail from the trailer to smash into the brother's face abd knock him out.
He doesn't kill anyone but he has an established pattern of abuse both physically and emotionally to the point where Eddy's emtire character was shaped by his abuse. As fir the physical part. He's an adult that severly hurt two boys, and in Eddy's case has been doing it to him fir years, and while the abuse is still played in a cartoony, slapstick manner ymthe trauma is played seriously.
None. He is a sadistic child abuser.