Orgrim Doomhammer's first act as warchief of the Horde was to crush the orc warlocks of the Shadow Council. He grudgingly spared the council's former master, Gul'dan, in exchange for the warlock's servitude; in turn Gul'dan promised to create a host of powerful new warriors to serve the Horde. After experimenting at length with the souls of the recently slain council members, Gul'dan successfully instilled the spirit of the necrolyte Teron Gorefiend into the corpse of a fallen knight of Stormwind. Thus, the first terrifying death knight was born. Gul'dan transformed other council members as well, creating unholy warriors who sowed chaos and fear throughout the land of Azeroth during the Second War.
Following Gul'dan's desertion and death, part of the Horde, including the death knights, retreated through the Dark Portal to Draenor. Most of the surviving death knights disappeared after Draenor's destruction, with the exception of Teron Gorefiend, whose restless and embittered form resides now in the Black Temple of Outland.