It sometimes feels like there are simply too many minor characters, shadowy mythical figures, and characters whose existence is merely hinted at to possibly keep up with on Game of Thrones. I am a show-watcher, book-reader, and internet theorizer and even I can't keep up with all the possible avenues this show could take us down. For example, who is the Elder Brother on Game of Thrones, and why is the internet theorizing about him?
The Elder Brother is a character that appears on the Quiet Isle in the books, and many book theorists believe that he is connected to the potential return of The Hound. The Quiet Isle is something of a monastery for men who take a vow of silence in an effort to atone for their sins. Brienne of Tarth journeys there with Septon Meribald and, of course, her loyal squire Podrick Payne, and she meets a mysterious gravedigger, and the Elder Brother.
According to the book, A Feast For Crows, the Elder Brother was once a knight and fought for the Targaryans at the Battle of the Trident. He was knocked unconscious and thought dead, so his companions stripped him of his clothes and dumped him into the river. Eventually, he washed up, naked, on Quiet Isle, and spent the next 10 years in silence. When we catch up with him, he is the leader of the silent community, known to be a healer, and the only inhabitant permitted to speak freely. He also appears to Brienne to be much younger than his title would imply.
When Brienne meets the Elder Brother, they discuss both his past, and her current mission. He seems to know a lot about the Stark girls, which some take as evidence that Sandor Clegane spent some time on the Quiet Isle. He knows, for example, that it was Arya Stark and not Sansa Stark who was taken captive by The Hound. He tells Brienne that The Hound is certainly dead, but much of the internet speculates that there's more to this statement than meets the eye. Elder Brother said that The Hound was dead, but didn't say that Sandor Clegane was dead.
As the Island is a place for repentance, it would be logical that when the Elder Brother referred to "The Hound," he meant only the evil, violent part of the man. Perhaps Sandor repented of his sins and let "The Hound" die, while he allowed the good part of his soul to flourish. Many even believe that the mysterious gravedigger Brienne meets is actually Sandor Clegane in disguise. His face was hidden after all.
Of course, all of this will play very differently on the show. But we do know that Sansa has just sent Brienne to Riverrun, near where all of this action is supposed to take place. It's possible that we could be seeing Sandor Clegane again very soon.