There's an increasingly popular fan theory out there that Bran Stark is really the Night King. And, when you think about it, it makes a lot of sense. Both are super creepy and have no personality. But jokes aside, people really seem to think that it's possible Bran got trapped warging into the Night King's body when he tried to stop the Children of the Forest from making White Walkers in the first place. But we all know nothing happens in Game of Thrones without George R.R. Martin's OK. So what do the Game of Thrones books have to say about the Night King?
Surprisingly, no such character exists in the books. The Night King is a creation of show runners David Benioff and D.B. Weiss, probably designed to make the White Walkers a more imposing and frightening force. In the books, unlike on the show, the White Walkers have remained, for the most part, an off-page threat. That's not to say that won't change, or that a Night King will never exist in the books — as fans know, Martin has been working on the next book in the series for a long time, and the show has eclipsed the series for the past two seasons. There's still a chance the Night King will appear in the next written installment.
Interestingly, though A Song of Ice and Fire doesn't feature a Night King yet, the books do contain a Night's King. Though it might seem like only a small grammatical difference, the two characters actually play vastly different roles. Here's what the books have to say about the Night's King:
He had been the thirteenth man to lead the Night's Watch, [Old Nan] said; a warrior who knew no fear. 'And that was the fault in him,' she would add, 'for all men must know fear.'
Yes, in the books the Night's King was tasked with protecting mankind by leading the Night's Watch, not destroying it as a White Walker. However, the 13th leader of the Watch might not have been as dissimilar from the show's Night King as we might imagine. As an article in Inverse explains:
The Night’s King supposedly fell in love with a cold woman with blue eyes beyond the Wall. Sounds like a female White Walker, though we haven’t seen any evidence of them in the show. He married her, styled himself the Night’s King and her the Night’s Queen, and ruled over the Wall for 13 years, sacrificing brothers of the Watch. Eventually, the combined forces of a Wildling King-Beyond-the-Wall and a Stark king took him down.
So, even though the Night's King isn't explicitly styled as a White Walker, it seems like he may have turned his back on humans in favor of his potentially inhuman wife. The things we do for love, right Jaime? It's possible that even though this mythical leader was ostensibly killed, he was resurrected by his wife as a White Walker. And Martin has been coy regarding whether the Night's King and the Night King might really be the same character after all. In response to a question from Game of Thrones Wiki, Martin said:
As for the Night’s King (the form I prefer), in the books he is a legendary figure, akin to Lann the Clever and Brandon the Builder, and no more likely to have survived to the present day than they have.
Although Martin mentions that the Night's King is most likely dead, he does throw in the fact that he prefers the spelling of "Night's King" as a opposed to "Night King" — a statement that might hint that in the show, they have been combined to become the same character. Maybe the reason White Walkers wanted babies as a sacrifice from Craster in the show was so the Night ('s?) King could have children with his off-screen wife. After all, infant wights wouldn't serve much purpose in the army of the undead. Unless, of course, they grow up to become White Walkers.
However, it's kind of improbable that the Night's King of the books is the Night King of the show, once you consider the fact that we've seen the creation of the Night King onscreen. He was stabbed in the heart with a piece of dragonglass by the Children of the Forest, definitely not killed by Stark forces and resurrected by a White Walker queen. It's completely possible Benioff and Weiss have dispensed with the idea of the Night's King altogether. After all, this is the second season that's gone beyond Martin's books. Perhaps the writers are feeling more comfortable making their own narrative choices, and the fan theory about Bran is correct after all.
Either way, there's no denying that the Night King is terrifying, especially now that he has an ice dragon. Watch out, Westeros. The Night ('s? Still unclear) King is coming for you.