Death Knight Lore
Shadows of Justice
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.
Champions of the Lich King
Years after the destruction of Draenor, the immensely powerful Lich King created a new breed of death knights: malevolent, rune-wielding warriors
of the Scourge. The first and greatest of these was Prince Arthas Menethil, once a mighty paladin of the Silver Hand, who sacrificed his soul to claim the runeblade Frostmourne in a desperate bid to save his people.
Unlike Gul'dan's death knights, modern death knights consist mainly of paladins who lost their faith and pledged their souls to the Lich King in exchange for the promise of immortality. Death knights who fall in battle are soon raised again to continue in their master's service.
In the years since Arthas shattered the Frozen Throne and merged with the Lich King, the power and fury of the death knights has only grown. Now these unrelenting crusaders of the damned eagerly await the Lich King's command to unleash their fury on Azeroth once again.