Game Of Thrones: 9 Fan Theories On How It Will End
3. Bran Saves The Seven Kingdoms
Bran may be one of the most powerful characters in all of Westeros, or potentially so at least. His training with the Three-Eyed Raven has led to him having visions of the past (and maybe the future), which in turn led to time-travelling (and that tragic Hodor reveal), and him then becoming the Raven himself.
Because of that, there are all sorts of Bran theories, such as him being responsible for the voices in the Mad King's head, or that he is every Bran Stark to have ever lived (from The Builder onwards).
The theory goes that Bran is going to continue developing his powers and gain more control over what he can do with them, essentially become some sort of time-travelling wizard. The theory is that he'll be the one who saves Westeros from destruction by the White Walkers or any other threat, by using his magical powers to help defeat them and restore balance to the world. Even within this there are a few different thoughts, such as him having been to an alt-future, and thus he came back and forced Jaime Lannister to push him from the tower, helping set in motion the Game of Thrones, necessary to stop the Walkers.