Ian McShane just can't quit HBO. The Emmy-winning British actor — who made waves as the most foul-mouthed character on the network's profanity-laden "Deadwood" — has joined the cast of hit series "Game of Thrones" in a mystery role for Season 6, according to Entertainment Weekly

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Of course, for fans of the series and George R.R. Martin's novels, it might not be that much of a mystery. There are a handful of as-yet-unseen characters casting long shadows that McShane could be inhabiting, and fans online have been doing plenty of  speculating. McShane is said to be playing "a very good part" that is "centrally involved" in a protagonist's storyline. Of course, given the number of protagonists there are on the sprawling series, that could be anyone. 

Or could it? The smart money seems to be on McShane playing Randyll Tarly, "one of the greatest soldiers in Westeros" and dad to lovable Jon Snow confidant Sam Tarly. If you need fearsome, grizzled and battle-hardened, McShane's your guy. Of he could be playing Euron Greyjoy, uncle to poor, castrated Theon/Reek (Alfie Allen). Casting notices for the role called for a "pirate" who "has terrorized seas all around the world," and McShane certainly has onscreen pirating experience.  

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But what if it's neither of them? What if, in response to the constant questions about whether or not Jon Snow is really dead, McShane is playing a brand-new character meant to represent HBO president of programming Michael "Dead is Dead" Lombardo, who will just show up every episode and say, directly into the camera, "No, he's dead. Really, really dead. For serious." It might be a departure from the books, by why not?

Follow Ned Ehrbar on Twitter: @nedrick