Update: Apparently there was some confusion, and Kristofer Hivju is not in Justice League. IGN has since corrected and redacted their original article after being contacted by WB, though apparently they were first told the concept art was of Hivju's likeness.
Kristofer Hivju, known for playing the Wildling warrior Tormund Giantsbane in Game of Thrones, is said to be playing an ancient Atlantean King in Justice League.
According to IGN, they spotted Justice League concept art featuring Kristofer Hivju with the label of an ancient Atlantean king.
It's speculated that Kristofer Hivju may be involved in a flashback scene involving a Mother Box.
It should also be noted that the cinematographer on Justice League, Fabian Wagner, is also the director of photography for episodes of Game of Thrones and was responsible for this past week's epic episode, "Battle of the Bastards," as well as this week's season 6 finale.
Jason Momoa was also featured on Game Of Thrones as Drogo.
"Justice League" has a November 17, 2017 release directed by Zack Snyder starring Ben Affleck as Batman, Henry Cavill as Superman, Gal Gadot as Wonder Woman, Jason Momoa as Aquaman, Ezra Miller as The Flash, Ray Fisher as Cyborg, J.K. Simmons as Commissioner Gordon and Willem Dafoe in an unknown role.
Fueled by his restored faith in humanity and inspired by Superman’s selfless act, Bruce Wayne enlists the help of his newfound ally, Diana Prince, to face an even greater enemy. Together, Batman and Wonder Woman work quickly to find and recruit a team of metahumans to stand against this newly awakened threat. But despite the formation of this unprecedented league of heroes—Batman, Wonder Woman, Aquaman, Cyborg and The Flash—it may already be too late to save the planet from an assault of catastrophic proportions.