One of the more prevalent fan theories swirling around the pending eighth and final season of Game of Thrones suggests that the fearsome Night King, leader of the White Walkers and King of the Dead, might have been someone closer to the cast than anyone realized.
Many fans believe that Bran Stark will be revealed to have a deeper connection to the Night King, with some even believing the magically-empowered Stark boy will turn out to be the villain himself. Despite the prevalence of the theory in recent weeks, it may have actually been disproven months ago.
The King Who Waited
Bran Stark has gone through one of the most unique journeys of any character in the Game of Thrones universe. While most of the cast have been dealing with political strife and power struggles, Bran has spent a great deal of the series beyond the Wall. He's learned about the magical forces of the world, and even tapped into those elements himself. By inheriting the powers and title of the Three-Eyed Raven, he's gained the ability to see through time and space, peering into the events of the past. He's also proven to be able to interfere with the past, as he did when he accidentally altered the fate of the loyal Hodor and led him to his eventual death.
A consistent fan theory in the lead-up to the final season has suggested that Bran will use those powers to time travel back to the early years of Westeros. In doing so, he'll become entangled in the past even more so than before and end up possessing the man who becomes the Night King. It's an interesting theory, tying the main villain of the series even closer to the people who stand against him. And it's not without precedent.
Bran previously used his ability to look through time to watch the Children of the Forest turning one of the First Men into a White Walker, setting up a battle that would be fought thousands of years later. His powers also caused changes to the past, like with Hodor and how he could "warg" into people and animals to control their actions. But this theory seems like an extreme expansion of that power, and would seem out of place even in the mystical world of Westeros.
Beyond that, there's also the fact that actors and directors from the series may have actually refuted the theory months ago.