Want to know the history/lore of the Death Knights and how they fit into the World of Warcraft? WoW Insider have written up a nice little piece...

With all the hubbub about the Wrath of the Lich King expansion, Know Your Lore is going to cover some of the lore behind our frozen neighbor to the north. (No, not Canada. They have no history. Also, I fully expect to get gkicked for that statement.) We already took care of Arthas and Sylvanas, but we still have Ner'zhul, Anub'arak, and others to cover.