I have no idea, but I know that his name is Johan Liebert and it's generally implied that he's a manipulative bastard and a sociopathic monster. Hence the title of a manga I don't read.
If you say Tucker is close, then that must mean they performed evil experiments and/or abused their own families, since Tucker did both at the same time.
Anyway I'm not sure what to say for the most evil villain, but if I had to guess I might say Johan from Monster. And here's the thing: I haven't even READ Monster, but Johan's reputation precedes him.
