Willem Dafoe / Jason Momoa

Back in April, we heard that Willem Dafoe would play an unspecified "good guy" in Justice League, without any details on what character that might be. This past summer, we began hearing that Dafoe would be portraying Nuidis Vulko, a trusted advisor to Aquaman (Jason Momoa), and would also be joining the cast of Aquaman as the same character.

Now Dafoe has clarified the roles he will play in each movie. He told The Guardian: "Justice League is very particular because it’s an ensemble movie and my character is being introduced here in order to be a principal role in Aquaman." That suggests Nuidis Vulko may be something more than simply a science advisor in Aquaman.
 
The character first appeared in DC comics in 1967, establishing himself over time as a notorious academic and political figure, involved in many political changes in Atlantis. Of course, the movie is not beholden to past incarnations of any of the characters, but there's quite enough comic book evidence to suggest that Vulko can be a good guy with his own ideas on how Aquaman should deal with challenges to Atlantis.
 
Dafoe has appeared in more than 100 movies and TV shows over the past 35 years, earning two Academy Award nominations for his performances, first in Platoon, then in Shadow of the Vampire (below).

He remains an in-demand actor, in large part because he dedicates himself to every role, no matter if it's big or small. Comic book fans remember him primarily because of his villainous turn in Sam Raimi's Spider-Man movies as Norman Osborn, also known as Green Goblin; he was certainly a tortured bad guy in those appearances.

We're expected something completely different from Dafoe as Vulko, first in Justice League, due in theaters on November 17, 2018, followed by Aquaman, scheduled to bow on July 27, 2018.