Rise of the Thrall Lord
One of the original Thrall Masters, Vanalor was the The Master of the Dead. He was known to have the ability to command any undead creature or creatures imbued with negative energy.
A millennium ago he was a Paladin and an adventuring companion of Gaither, Devian, Arkus, Valgar, and Larketh and led the ill-fated counter-assault on the Abysmal Plane of Shaddonon that ended the Third Demon War.
Little is known of his corruption to a Death Knight or how he became a consort to the Goddess of Death.