Apocalypse

Apocalypse is the artifact used by unholy death knights in World of Warcraft: Legion.

Source
This item is a quest reward from The Dark Riders (death knight).

Background
''Vampiric demons known as nathrezim forged this ancient sword, which brings with it violence, plagues, and death. Apocalypse soon earned a horrific reputation in the hands of a Tirisgarde mage who couldn't control its destructive energies. In time the sword was seized by the malevolent Dark Riders: servants of Medivh, the corrupted Guardian of Tirisfal. They hid the blade in the catacombs under his home, the tower of Karazhan.''