Daggus, the last Avatar of the Dark Side.
The Avatar of the Dark Side was supposed to be a man who would carry the true power of the Dark Side of the Force, and with it, he would harvest the power to become the ruler of the Galaxy, the ultimate tyrant with eternal and unstoppable power.
The only Avatar of Dark that history has a record of is Darth Daggus, a human male Sith Lord; who was defeated by Hei-Ri Devon, the Avatar of the Light Side.
The coming of the Avatar of the Light Side was predicted in the Avatar's Prophecy, written by the Dark Lord Izenghar.