Warhammer: Shadow of the Horned Rat
Shadow of the Horned Rat is the first Warhammer game created for the PC and the PlayStation, and one of the most groundbreaking computer games in history. It is a Real Time Tactics game, and one of the most unique of its kind (along with Command & Conquer). Although it is considered groundbreaking, it is often criticised for its immense difficulty.
Though not technically supposed to lead up to it, Dark Omen is considered to be the sequel to this game.