...yes, leather armor!
Warlock is an evil class and rather unique for WoW in that the Warlock is power-hungry and harnesses felenergy while suffering the taint of it. The Warlock also commands forces from the demonic plane.
Nothing is more satisfying than sucking the soul out of the skull of the Warlock's adversary! Also the sweet, sweet self-inflicted pain of Lifetap! Ah, what the Warlock won't endure for more power!
So, what couldn't be more natural than clothing oneself in leather? A Warlock wants the option of wearing leather armor (particularly some nice black S&M leather mmmm!).
This has always been a miss from Blizzard, according to lore, the Warlock is a corruption of the Shaman class, and Shamans wear leather!
Thank you for reading.
/Sillywizard