Adewale Akinnuoye-Agbaje is most famous for playing Mr. Eko on Lost, but when not talking to Smoke Monsters, he’s had a successful career, appearing in Thor: The Dark World, The Bourne Identity, and Oz. He’ll return to HBO next year as Malko on Game of Thrones. Who’s Malko? Well, no one knows — as Vulture notes, he doesn’t “appear anywhere in George R.R. Martin’s books.”
My best guess is Moqorro, a very tall and very intimidating red priest, though considering how many things are changing from the books to the show, he might as well be Rickon Stark.