They referred to the main character repeatedly as a male witch, not a warlock. I think the dragon was gold, and a pet. I think each book had a different dragon's name as the title. Each cover was a different color (?), there were maybe 5-7 books in the series, published between 1990-2005. The main antagonist in the first part was a necromancer. There was a sea port town in middle, robbed a tower towards the end?
This is not Eldest or Eragon series. Maybe a male author.
Also not the Vlad Taltos series, although it looks super cool, judging by the first few chapters of the story. If I recall correctly, the intro of the one I'm looking for takes place in a small town, where this necromancer is kind of the mayor... maybe a garden, some tunnels. The first scene I think is the dude and his dragon in the wild regions around said town. He wasn't an assassin, I don't think, and the thieving was for something specific, not a job. Doubtful this guy would have been in a guild or the like, very much a ranger/druid loner... hopefully edging closer; that name Jhereg is driving me batty though.