What mental illnesses would this person have?

Person in question; they change their moods alot, could be acting friendly and laughing but the next second becoming violent and screaming/being very angry.

Finds it funny when killing people and likes to torture them, (makes it out as a game sort of, joking with his victims and playing pranks on them, for example telling someone he is giving water to them but he pours spiders on their face instead and laughs about it.) Very domineering and doesn't like his authority being questioned (if he feels threatened he'll most likely shoot them.)

Despite that he is very friendly to his men/friends and jokes/plays around with them, doesn't like newcomers though. What mental illnesses do you think this person has?