Spoilers for the Game of Thrones ending below!
At long last, the question of who will sit the Iron Throne at the end of Game of Thrones has been answered. Many intelligent and ruthless characters tried to manipulate their way to power through the course of the show, only to fail--and die, often horribly, as is the way of the game. Fans, viewers, and Las Vegas speculated since it all started about who would live to rule Westeros (and take everyone else out along the way), and all sorts of callbacks, references, and Easter eggs have provided clues for fan theories over the years.
So the fact that it was Bran Stark who wound up the ruler of Westeros in the finale episode is somewhat confusing. He's an entirely unassuming choice, having seemingly done very little since he became the new Three-Eyed Raven way back in Season 6. Though Bran has the ability to warg into animals (and sometimes people) and to know about seemingly anything that's happening anywhere, he seems to rarely use these powers, and hasn't been very involved in the goings-on of Westeros. He outed Littlefinger in Season 7, provided some information about dealing with the Night King, and helped Jon learn about his true identity, but that's about it. Bran came off as a good choice for the ruler of Westeros because it's seemingly not a job he wants ("I don't really 'want' anymore," he said earlier in Season 8), because he's supposedly wise, and because he's distant and therefore can be objective and just.
But some viewers are questioning the choice of Bran in the end, because it doesn't make a ton of sense. For someone who knows seemingly everything, Bran hasn't spent much time this season helping anyone. He did little during Season 7, he did nothing during the Battle of Winterfell, and what information he has provided hasn't been all that useful. What makes him such a good choice for king, other than the fact that he's a great compromise to keep the power away from everyone else?
The fact that Bran hasn't had much going on since Season 6 has bothered a lot of viewers, and now to have him wind up on the throne seemingly by default is even less satisfying. Bran does say one thing that suggests he knows more than he's letting on, though. During the council to choose the new king, when Tyrion asks Bran if he's up for the job, Bran responds, "Why do you think I came all this way?" Once again, Bran suggests he knew something would happen before it did, so why isn't he using that information more effectively?
If you think about it, Bran's actions--and more aptly, his inaction--have constantly and subtly pushed in the direction of him becoming king. Season 8 makes a lot more sense if you consider that Bran might have been manipulating events for his own benefit all along. After all, he could have saved a lot more lives along the way, if that had been his goal. But what if it wasn't?
Bran the Deceiver
Consider Bran's actions during the Battle of Winterfell. Though he can warg into animals and get a bird's eye view of the battle, which could then allow him to pass useful intelligence to the fighters defending the castle, Bran does nothing. He just sits in the godswood, quietly using himself as bait for the Night King. If he could have helped, why didn't he? Maybe because Bran foresaw several key deaths that would help bolster his position.
The Battle of Winterfell saw so many of Daenerys's forces eliminated that she was suddenly on even ground with the Lannisters. She also lost Jorah Mormont, her most trusted adviser and most capable protector. Other key deaths during the battle included a popular and capable leader in Lyanna Mormont, who was known to sway public opinion with gripping speeches, and Theon Greyjoy, who had a history with Sansa Stark that could divide her loyalties. Key people who might have changed the rest of the events of Season 8 were lost during the battle.
Bran also helps provide Jon with the information about his true parentage, even though that does nothing but complicate an already strained wartime situation. It's Bran who convinces Samwell Tarly to tell Jon the truth about who his parents were, which instantly puts Jon into conflict with Dany even though he's already pledged her his loyalty, bent the knee, and given up being King in the North for her. Jon has a better claim to the Iron Throne than Dany, but it's obvious he doesn't want to rule. Why tell Jon about his parents at all, or at least, why tell him right before he fights a battle that could mean the destruction of all of Westeros? It seems like a bad move that doesn't help anyone, unless you consider that Bran wants to sow discord and push Daenerys over the edge.
Losing Ser Jorah leaves Daenerys without her best bodyguard and without the man who had often acted as the voice of reason against her worst impulses, right when Dany is within sight of her goal, and right when the biggest threat to her claim to the throne, Jon, is suddenly revealed. Daenerys then loses her dragon Rhaegal and her close friend and adviser Missandei to a sneak attack at Dragonstone--again, something that seems like a guy who can become a bird and see things anywhere in the world could have helped her avoid.
That puts Daenerys at King's Landing in a fraught state. Her enemies have killed her best people, her advisers are turning on her, her dragons are dead, she hasn't won any loyalty despite helping beat the army of the dead, and the man she loves could challenge her pursuit of the goal she spent her life chasing. She's primed to do something terrible, and Bran could have stopped any or all of those circumstances from coming to pass with his superpowers. But he doesn't.
Playing The Long Game
Really, the events of Season 8 make a lot more sense if you assume Bran is manipulating people on purpose, Littlefinger-style. He tells Jon that he's actually Aegon Targaryen knowing that at the very least, it'll create distrust between him and Daenerys. He lets lots of people die fighting the army of the dead because he wants them gone, but sets up Arya to kill the Night King (he gave her that Valryian steel dagger, don't forget) to eliminate one of his chief adversaries. He allows Dany to lose her armies and her dragons to weaken her. He doesn't provide any of his family members with information about King's Landing or their enemies that could help them take the city with less bloodshed. Everything he does or doesn't do sets up the opportunity for Cersei, Dany, and Jon to eliminate each other, and nothing he does or doesn't do saves lives or de-escalates that conflict.
There's even a fan theory to go with this idea, but it's based more on George R.R. Martin's "A Song of Ice and Fire" novels than what's in the show. It concerns the true identity of the Three-Eyed Raven: a Targaryen bastard called Brynden Rivers, also known as the Bloodraven. With his greensight and warg powers, the theory goes, the Bloodraven could have lured Bran north of the Wall and then taken over his body, executing a lengthy plan to take the Iron Throne for himself. (Here's more about the idea of Bran becoming the Bloodraven.)
Fans have also speculated that Bran could become the Night King through some combination of time travel and magic ever since Season 6. The touch of the Night King has been enough to turn babies into White Walkers and dragons into wights, and the Night King pointedly touched Bran during a vision in Season 6 ("His mark is on me," Bran reminded us in Season 8). Maybe that touch had more of an effect on Bran than we all realized.
If Bran is evil, then his arc in Season 8 is a masterstroke of manipulation and careful inaction--everything Bran doesn't do matters as much as everything he does do. There's a reason he doesn't use his powers to help people in Season 8: He doesn't want to help them. And by doing very little, acting disinterested, and downplaying his magic abilities, Bran sets himself up to seem like an excellent choice for king. He gets the throne with no opposition because everyone else thinks it was their idea to crown him. Littlefinger couldn't have executed a better deception.