Grim is a most interesting... something. Fond of hanging around Sanctuary, he makes everyone nervous. They keep trying to find him a new haunt, but he likes it there.
Charged with training Nick on his powers, he has some methods the school board would definitely frown on. Nick’s not too fond of them either. But no one can ever turn down Death.
But Grim has a much higher agenda... and Nick is just the tool he needs to get what he wants.
Grim used to be the Horseman of Death, but as of Instinct he has lost this position (when Nick chose his new generals).