Vulko was created by Bob Haney and Howard Purcell. Vulko's a talented Atlantean politician who plays an invaluable role as a mentor (also the city's eldest dignitary) to Aquaman. Before Aquaman's reign, Vulko was around for his birth where he fought and argued against the curse of Kordax.
We're not sure just yet how much screen-time Dafoe will be getting, but we do know he's set to appear in the full Atlantean-royal costume.