Death knights are necromantic warriors who wield necromantic energies and the cold chill of death.
"Death knights. Human corpses animated by dead orc warlocks, they reeked of dark power."
The first generation death knights are soldiers of darkness that were created by the warlock Gul'dan to replace the slaughtered Warlock clans. Assembled from the corpses of the Knights of Azeroth slain in the last battles of the First War, these abominations were then instilled with the ethereal essence of the Shadow Council. Furthered empowered with the magical energies culled form the slain Necrolytes, the Death Knights wield an arsenal of necromantic and elemental spells that mete out all but certain death to the enemies of the Horde.
After the Horde's defeat in the Second War, Ner'zhul sought to reinvigorate his followers by opening gateways to new worlds for them to conquer. To that end, he dispatched his servants to recover various artifacts from the Tomb of Sargeras, including the scepter, which the fallen titan had used to infiltrate Azeroth centuries before. Ner'zhul was not Sargeras, however, so he could not simply command the staff to open portals. He had to wait until the constellations of Draenor were properly aligned, and he could only use the scepter in conjunction with other artifacts. The warlock grew impatient, frustrated with his limitations. Intoxicated by the Skull of Gul'dan's influence, he had visions of his erstwhile apprentice, who urged him to unleash his godlike powers. When at last the moment arrived for Ner'zhul to act, he did so with wild abandon, heedless of the consequences. It mattered not to him if Draenor was destroyed; in fact, he welcomed it as part of his legacy. With the scepter, he blasted hole after hole through the fabric of reality, shredding the seams connecting Draenor to the rest of the physical universe. As he rushed headlong through one of the portals, he could hear the world shattering behind him.
Just as Ner'zhul and his followers entered the Twisting Nether - they were ambushed by Kil'jaeden and his demonic minions. Warped by the demon's chaotic powers, Ner'zhul became a spectral being of unfathomable power. At that moment, the orc known as Ner'zhul was shattered forever, and the Lich King was born. Ner'zhul's loyal death knights and warlock followers were also transformed by the demon's chaotic energies. The wicked spell casters were ripped apart and remade as skeletal Liches.
The Death Knights of the Scourge
Death Knights were once heroic, virtuous defenders of humanity. However, they were corrupted by the subtle machinations of the Lich King and lured to his dark standard. These former heroes were given untold power and the promise of immortality in exchange for their loyalties. Although they retained their humanity, their twisted souls were bound to the Lich King's will for all time. Bestowed with black, vampiric runeblades and shadowy steeds, death knights now serve as the Scourge's mightiest generations.
Third Generation Knights