Following the Game of Thrones Season 7 finale, a fan theory hit the net suggesting that Bran Stark is actually the Night King, and that the Night King's Army of the Dead formed the Stark Sigil.
There is potential evidence to back up the claim in that Bran Stark and the Night King seemingly wear the same clothes and even resemble each other. There is also the fact the two are both involved with magic, and also that Bran Stark has gone back in the past and affected both the past and future (Hodor), so arguably nothing can be ruled out.
Vulture caught up with Game of Thrones Bran Stark actor Isaac Hempstead Wright who commented on Season 7 as well as the theory that Bran Stark is the Night King, who says the two are different characters.
I think it’s less that they’re the same person and more that they’re two of the ancient beings of Westeros. The Three-Eyed Raven has been around for God knows how long, and White Walkers have been reported since the beginning of time. As we’ve seen, they were created by the Children of the Forest, so we can’t get much more ancient than that. Perhaps we can think of it as these are two characters with a huge amount of power, but one is a Frankenstein’s monster who is driven by nothing but hatred and violence. Then there’s Bran, who uses his powers for good. I want to find out why the Night King is so obsessed with destroying mankind. We’ll see whether they have any kind of explanations in the next season. Hopefully we’ll find out cool stuff about both of those characters.
While the title of Vulture's article states Bran Stark as the Night King has been debunked by Isaac Hempstead Wright, fans should keep in mind that the unlike the Three-Eyed Raven, the actor doesn't know everything that is going to happen.
During shooting I have to be like, “Nope, I can’t say anything.” But this is the golden period. We haven’t gotten the scripts for the next season and this one’s just finished. I can properly theorize and chat, because I don’t know anything that’s going to happen.