Earlier this season, Game of Thrones fans got a look at the home of the enigmatic White Walkers. The ghastly snow zombies appear for just a few minutes each season, but that hasn’t stopped them from becoming some of the most visually iconic creatures on the show. While the Walkers may appear to be pure computer-generated wizardry, they’re actually played by actors caked with prosthetics and makeup. As one of the Walkers, Ross Mullan has snatched babies, faced off against members of the Night’s Watch, and even led an army of reanimated corpses on horseback.

Mullan, 47, compares working behind heavy makeup to training for traditional mask theater in Ottawa, Canada (he now resides in London). "I trained with masks in drama school and then joined a mask theater company," he says, noting that acting with masks goes back to ancient Greece. It’s a complicated skill unto itself; wearing a wolf mask, for example, immediately tells the audience what you are, but it also obscures an actor’s most valuable tool. “[Working with masks] taught me how to bring things to life using something other than my own face,” Mullan explains, “taking the inanimate and bringing it to life."