motivating a necromancer

Have a necromancer whose purposes are clear, at least.  Assassinations and enslaving people by magic feature.

Except there really does need to be a motive behind it.  Revenge, and if so, for what?  The quest for knowledge, even if wisely forbidden?  Who knows?  Greed might be a possible motive.

Haven't even decided whether male or female.  Perhaps I should count noses and decide after I give the other stories their villains and villainesses.  Villainy being equal opportunity.