Jimmy never had a body, He was never born, He can't even really count as a demon. Due to this, Jimmy is forced to take the form as people, or even possessing them.

He never had a personality, he adapted to his surroundings.
It's why he kills people, he only kills people who have "sinned". Though hes judgement are always harsh which is why people in the gmod world see him as evil. He has killed alot. (Literally everyone in the Gmod universe has killed at least once)