Khôragan might have been most recent Dark Lord. 220 years after the fall of Sauron, An easterling rose to power as dark lord this was him. He probably also leaded the Black Easterlings while he was just a Rhûn's general.
He is a character created in a modification for the video game BFME2 (Battle for Middle-Earth II: Rise of the Witch-King).
Khôragan as depicted in BFME2