We now have a much better idea of who he will play in Season 6.

Ian McShane will appear on one episode in Season 6.
We already knew Ian McShane would only be appearing on one episode of the series, which he confirmed in his latest interview with PopGoesTheNews. And we knew he would not be Randyll Tarly or Euron Greyjoy after those roles were cast as other actors.
However, in his interview Ian McShane revealed, “I am responsible for bringing somebody back that you think you’re never going to see again. I’ll leave it at that.” The first thing on everyone’s minds about bringing somebody back is probably Jon Snow and his brutal stabbing at the hands of the Night’s Watch in the Season 5 finale.
But there is already plenty of evidence that this will happen via Melisandre, and you’d expect Jon’s savior to stick around a little.
Plus, there are a lot of other dead characters that could be resurrected, and there’s evidence in George R.R. Martin’s novels that some will be.
But there’s one character in particular that seems most likely. So we’re ready to call Ian McShane’s Game of Thrones role confirmed (unofficially) as the Elder Brother. Who is that, and how do we know it? Let’s play a little game of questions and answers to find out.
Who else can raise the dead? Well, the Night’s King can, possibly other White Walkers, but this would seem like a waste to have Ian McShane cameo as a White Walker. Besides, McShane has already said that his role is important and another White Walker who can raise the dead or another Red Priest probably wouldn’t add much.
But what did McShane say exactly? “I am responsible for bringing somebody back.” Back from what? The implication is “the dead,” but he could be bringing them back from imprisonment (like Margaery), madness (like Theon), or even near-death (any number of people we didn’t officially see die on screen).
According to the Gravedigger theory, that someone is the Hound, Sandor Clegane.
The Gravedigger theory says that the Hound didn’t die after his battle with Brienne; instead, he was nursed back to health in the care of a monastic order of the Seven, reformed himself, and become a Monk of the Seven Gods. That sounds a little crazy, but the show is actually pretty careful to show the Hound as a compassionate and caring soul despite his brutality. The Gravedigger theory mostly works as an epilogue to Sandor Clegane. He had a lot of inner demons as the knight known as the Hound, and as that persona dies to some pretty serious physical trauma, Sandor gets a psychological respite and an implied happy ending to his story.
Key to this transformation is the Elder Brother, the head of the monastery, and the only brother not sworn to a vow of silence. He’d be the natural teacher for a reforming Sandor, but probably wouldn’t figure into the wider politics of Westeros, just a key figure in the transformation of a character who might not be done making an impact.
Ian McShane is a one-episode character (or at least, someone of roughly that shooting length; the character could still show up in a couple episodes, if only for a few moments in one) of vital importance who brings someone back who we thought we were never going to see again. The Elder Brother fits the build.
But there is another reason it could be extremely important that Sandor Clegane is alive, other than as a holder of information: Clegane Bowl. As Alt Shift X points out at the end of the video above, there is a fan theory called Clegane Bowl that centers on the Gravedigger theory being correct and Ser Robert Strong being the reanimated Mountain.
Cersei has a Trial by Combat coming next year (most likely), and if the Clegane Bowl theory is correct, the two combatants would be Ser Gregor Clegane, “The Mountain,” now a zombie, and Sandor Clegane, formerly “The Hound.” The Mountain is the obvious choice for Cersei. She used him before in “The Mountain and the Viper,” and despite being poisoned and sort of dying, he won the Trial by Combat. Who can actually face off against the Mountain and have any sort of chance?
Clegane Bowl states that the champion of the Faith will be the Hound. The Hound has hated his brother since he pushed his face into the fire as a child. This would make sense for his character if his transformation is not genuine, or even if it is and he is simply the best single combatant the Faith can muster. If the Hound has not truly given up his anger and become a man of peace, this would make sense in his character arc. He gets what he wanted, to fight and kill his brother or die trying. But most fans probably want his transformation to be genuine, and that makes the most sense in terms of George R.R. Martin’s masterwork. However, it would be really awesome. So even if it doesn’t happen in the books, (as the Hound vs. Brienne didn’t), then maybe we could still see Clegane Bowl.
Ian McShane on Game of Thrones
“[It’s] a one-off episode. That’s why I did it. But I can’t reveal anything, otherwise I will never work again.” But despite it being a one-off role, it is of vital importance, and McShane will bring back a character we thought we’d never see again. This is all just speculation, but it sounds like Ian McShane may be the Elder Brother and that his appearance will either resolve the Hound’s story, or it will set up Celgane Bowl at Cersei’s Trial by Combat. Either way Ian McShane will be shaking things up come Season 6. Winter is Coming, and it can’t come fast enough…