To be a warlock is to sell your soul or pledge your life to a generally not nice superpowerful being.  Why on earth or any other world would you do that?  Having a good reason for it is the core of your character's personality.  Let that guide your character development.  I played a neutral good rogue who became a warlock of Malcanthet because the Demon Queen of Succubi had possessed another party member, and my rogue agreed to the pact in exchange for Malcanthet freeing the other character.