His name? Jedi Master Jorus C’baoth.
Actually, wait. This might be a crazy idea, but what if it was Sifo Dyas, instead?
My idea would be to go for an ancient name, like Ulic Qel-Droma or Freedon Nadd. The reasoning here would be to sell the new threat as the return of a truly ancient anti-hero/villain leading the enemy faction of the ST, an order that Palpatine/Vader never knew about and was behind some events of the PT and OT.