Winter has finally come for HBO's smash-hit fantasy series, Game of Thrones, with the upcoming eighth season set to be its last. Based on George R. R. Martin's novel series of the same name, the show reinvigorated interest in the high fantasy genre that really only the likes of old favorites like Tolkien's Lord of the Rings and C.S Lewis' The Chronicles of Narnia have ever managed to draw. From Vikings to OutlanderGame of Thrones' departure from our small screens leaves many pretenders to the Iron Throne in its wake. But before the show shuffles into the cold, dark night like a marching White Walker, there's still the small matter of figuring out what the hell is going on with one of its most terrifying and fascinating characters: the Night King.

This frosty and silent figure has been slowly leading an army of the dead southwards to the Wall -- mankind's last defence against the mysterious perils of the most northern tip of Westeros. From flashbacks, we know that he was once one of the First Men who was magically transformed by the Children of the Forest to become the blue-eyed villain now poised to invade the domain of the living. We know that he's capable of recruiting the recently deceased to his cause, but we don't know how. We know that he's intent on fighting the descendants of the First Men, but we don't know why. We know that he was once flesh-and-blood, but we don't know whose flesh-and-blood. So many questions remain, and with just a few episodes left, how many answers can we expect?

15 THE NIGHT KING SET A TRAP FOR DAENERYS

The Night King riding a dragon in Game of Thrones

In one of the most tense arcs of the entire show, Jon Snow formed a ragtag Expendables-esque crew to gather proof of his claim that the greatest threat to the Seven Kingdoms wasn't power-hungry Lannisters or Targaryens, but an army of the dead. As expected, things took a turn for the worse, leaving #TeamSnow stranded and surrounded by the Night King's forces.

Despite having the King in the North right where he wanted him, the King didn't attack. Why? Redditor DamisuNight'sKing thinks he was waiting for Dany to swoop to her ally's rescue so that he could poach one of her dragons and tear down the Wall. After all, why else would the King conveniently have dragon-felling spears with him?

14 THE NIGHT KING IS A STARK

Stark Family Game of Thrones

The Stark family are the most closely tied to the Night King, and for more reasons than just their proximity to his land. In the books, the original name of the Night's King -- as he's known -- is revealed to be Brandon Stark, explaining why their family motto became "Winter is Coming." In the show, redditor ThouCantTouchThis points out present-day Brandon Stark and the Night King share warg abilities.

Even the Wall has strong Stark ties, as it was said to have been erected by Bran the Builder. Megatron_McLargeHuge surmises that the TV Night King must also be an immortal Stark whose journey will end in him taking his rightful place as King in the North; mobilized by the scattering of his ancestors from Winterfell.

13 THE NIGHT KING WILL CONTROL THE MOUNTAIN

The Mountain holding Cersei in Game of Thrones

The stewing rivlary between brothers, Sandor "The Hound" and Gregor "The Mountain" Clegane, has long been expected to result in a climactic confrontation, dubbed "Cleganebowl" by fans. At one point, it looked like the fires of their feud were snuffed out when Gregor met his untimely end. Thanks to some necrotic science, however, The Mountain was revived as Cersei's personal zombie guard.

But, if Cersei were to ever bring her Frankenstein's knight north and within the Night King's range -- possibly to escape King's Landing -- fans have theorized that he could be undead enough for the King to take control of him. That would certainly up the stakes even higher for Cleganebowl.

12 THE NIGHT KING IS A MASTER WARGER

Game of Thrones warging

Like a frozen Pied Pier, the Night King seems to be able to magically reanimate an immeasurable number of corpses, which is a terrifying party trick for any who stand in his way. One minute you're fighting alongside your friends; the next, you're fighting their brainless bodies. But, who's to say that's really how it works? Maybe the wights are actually warged soldiers.

Arya_Granger posted this theory to reddit, pointing out the visual similarities between Bran warging into people's bodies and the Night King resurrecting them. People who are no longer alive have no pesky consciousness to overwhelm, making them easier targets. She also adds that wargs are attuned to one another -- which the King and Bran clearly are.

11 THE NIGHT KING ISN'T EVIL, HE'S NATURAL

Game of Thrones White Walkers

The "Winter is coming" tagline isn't just a weather warning, it's also a cheery reminder of our own mortality. Nothing can stay warm and vibrant forever -- the end, like the changing of the seasons, is inevitable. But, it's also part of a natural cycle, one which some fans think is best represented by the looming threat of the Night King.

Perhaps we're wrong to label him as a straight-up villain when we know he was created for a single purpose by the Children of the Forest. He was born to help them battle the First Men, which, in his mind, is still his primary mission. Just like Iron Man's creation of Ultron in the MCU, the Children wanted a champion, but their progeny outgrew them.

10 THE NIGHT KING CAN SEE THE FUTURE

three-eyed-raven game of thrones

Greenseers are highly respected and rarely found people who can see events that will happen, have happened or are happening right now through what the Children of the Forest refer to as "green dreams." The most notable greenseer was the Three-Eyed Raven, a title and ability that has since been passed on to Bran.

The former Three-Eyed Raven was taken out by the Night King, and as redditor Elvis_burrito suggests, this might have been a greenseer-on-greenseer crime. The Night King does have a knack for being in the right place at the right time, like predicting that Dany would bring her dragon over the Wall and knowing when Jon Snow was at Hardhome. This would also account for his physic link to Bran.

9 THE NIGHT KING THINKS A TREATY HAS BEEN BROKEN

Game of Thrones Jon Snow

In the legends of Westeros, a figure known as The Last Hero was said to have defeated the White Walkers long ago during the War of the Dawn. The implication is that this was done on the battlefield, but redditor c_forrester_thorne offers a different perspective. Maybe The Last Hero, when faced with an unbeatable enemy, negotiated a peace treaty between the First Men, Children of the Forest and White Walkers.

All three parties agreed to live separately in peace, until recent events plunging Westeros into chaos -- the appearance of dragons, the rise of the Lord of Light and humans encroaching on White Walker territory --  might have led to the Night King believing the terms of the treaty had been breached, prompting him to retaliate.

8 THE NIGHT KING IS RHAEGAR TARGARYEN

Game of Thrones Rhaegar Targaryen

Ever wondered how a being that appears to be the personification of winter itself can casually trot through flames, unharmed? Immunity to fire is a uniquely Targaryen trait, something that hasn't gone unnoticed by reddit user Three_eye_raven_s. This fan has a wild theory that the Night King isn't a Stark -- he's a Targaryen. Specifically, Rhaegar Targaryen.

The theorist argues that Rhaegar's demise was never confirmed on-screen, meaning he could well have lived through the Battle of the Trident to be coronated as the current Night King. If true, it would give new poignancy to the extended looks he exchanged with his illegitimate son, Jon Snow, and make for an emotional climax in the upcoming war.

7 THE NIGHT KING AND BRAN WILL FIGHT PSYCHICALLY

Game of Thrones Bran Night King

You've heard of Cleganebowl but what about... Mindbowl? Psychic battles are a well-known convention in everything from fantasy, to sci-fi to superhero media. We know that the Night King is able to interact with Bran on a mental plane of existence, so if Bran is able to hone his abilities, he could become Game of Thrones' Professor X equivalent.

The Mindbowl idea was suggested by redditor YezerIRL, who predicts the Night King being attacked on two fronts: in the physical world by Jon Snow and in the astral world by his brother, Bran. This joint offensive could be the only way to fell an adversary who seems to have a foot in the tangible and intangible.

6 THE NIGHT KING WILL BE REPLACED

Game Of Thrones Jon Snow White Walker fight

According to the followers of the Lord of Light, a mythic figure called Azor Ahai -- possibly an alternate version of The Last Hero -- created and used a sword known as Lightbringer to vanquish the Great Other, a god of cold and darkness. However, in order to activate the weapon's fantastic power he had to sacrifice the woman he loved.

R'hllor lore foretells that Azor Ahai will be reincarnated as The Prince That Was Promised. If the new Azor Ahai faces the Night King, redditor AnghkoR theorizes that he would have to turn the dragonglass he pulled from the Night King's chest on himself in order to command the wight army, taking the King's place and making a similarly selfless sacrifice as his forebear.

5 THE NIGHT KING IS AZOR AHAI

Game of Thrones Melisandre

What if the Night King isn't the ancient evil fated to be slain by Azor Ahai, or The Last Hero or The Prince/Princess That Was Promised? What if he is the hero of the story? It's natural for us, the human viewers, to empathize with the humans we see in the world of Game of Thrones. All of Westeros' prophesied saviors also come from human sources.

Reddit user OjWasFramed12 points out that the Night King has already checked off a key box that would qualify him to be the new Azor Ahai by reawakening Dany's dragon, Viserion. From the Night King's perspective, humans are Westeros' greatest threat, meaning destroying them would be to destroy evil -- as Azor Ahai is destined to do.

4 THE NIGHT KING IS A WELL-INTENTIONED EXTREMIST

Winter King at the Hardhome Massacre on HBO's Game Of Thrones

Well-intentioned extremists are villains who believe their terrible actions are justified because they're doing them for the greater good. This could be applied to the Night King, riffing on the ideas that he's a force of nature simply carrying out his job, or the hero of his kind like Azor Ahai.

One fan even goes so far as to suggest that he's "one of the most benevolent rulers in the entire world. Every single one of his men follows him loyally [...] and neither he nor his men have ever once tried to harm someone who wasn't trying to harm them first." They go on to hypothesize that his real mission is to rid the Seven Kingdoms of corruption to usher in an era of uninterrupted peace.

3 THE NIGHT KING WAS THE FIRST NIGHT'S WATCH COMMANDER

Game of Thrones Night King

The Night's Watch are meant to keep a keen eye on any activity north of the Wall, but is there a stronger connection between the watchers and the watched than we realize? After seeing the episode, "Hardhome" in Season Five, one theorist on reddit noticed that the insignia on the Night King's clasp could have hidden meaning.

They maintain that the clasp symbolizes a bird's skull -- possibly a raven's -- with a the cylindrical shape of a castle's turret in the middle that could easily be from Night Fort. It could have originally been worn to mark the wearer as the first ever Lord Commander of the Night's Watch. The King's armor and regal status must have come from somewhere, too.

2 THE NIGHT KING CAN ONLY BE DEFEATED BY JON SNOW

If you believe that Jon Snow is The Prince That Was Promised then you believe that destiny dictates that he will slay the Night King. However, redditor frowat takes this one step further. Not only will Jon be the one to do it, he's the only one who is able do it. The theory rests on the Night King's perceived greenseer ability.

The fan explains that when Jon's brothers turned on him, his story was supposed to end, making his revival completely unpredictable. This could explain why the King missed Drogon after easily spearing Viserion. The King didn't foresee this as it was Jon who ordered Dany to leave on the dragon. Jon's unpredictability could be the King's undoing.

1 THE NIGHT KING IS BRAN

Game of Thrones Bran Stark

This theory gained popularity when it was revealed that Bran's Three-Eyed Raven gifts enabled him to travel through time and possibly influence events. In fact, there's nothing to say he couldn't have already attempted this. Fans posit that Bran first journeyed back to tell King Aerys he should "burn them all." The Mad King unfortunately didn't understand that he was talking about White Walkers.

Bran would then be forced to travel further back to build the Wall as Bran the Builder, and then even further to warg into the First Man who became the Night King. As we saw with Hodor, time travel doesn't always go smoothly, and his failure to stop the transformation could have left Bran trapped; twisted into a new identity.