[quote=@DJAtomika]
[@Theunknowable]I am quite unsure of the Warlock's motives at the start of the conflict. Enlighten me a little? 
[/quote]

Unknown.  The story says that he worked for Xalafoor, but it doesn't say why.  Of course, it's 3000 years old and passed down by word of mouth, so it can't be very accurate or detailed.

I was thinking greed for the first one, with Xalafoor giving him powers in exchange for his service.  You'd have to have a reason why he was chosen, and so many others were killed, though, such as him being the son of a necromancer or something.  You can use any reason you want for these, though.  The past story doesn't matter so much, as it's not who we are any more and will only have minor influence on the future outside of what we learn about Xalafoor.