This is a thought that occurred to me, like many great thoughts do, as I was getting ready for work one day. According to Twitter (where, naturally, I immediately went to share this thought) it was actually the morning of my most recent birthday, which means I must have been granted access to some vein of cosmic truth as a gift from the universe. Therefore, you can just assume that everything in this post is absolutely, one-hundred-percent correct and should be taken as canon for both series. So, without further adieu, my theory:
Gerion Lannister is Godric Gryffindor.
Godric Gryffindor is, as I'm sure most of you know, one of the four legendary founders of Hogwarts School of Witchcraft and Wizardry in J.K. Rowling's Harry Potter series. Gerion Lannister is more obscure: he's a minor character (mentioned only) in A Song of Ice and Fire, the fantasy series by Bayonne's finest, George R. R. Martin (which I'll refer to as ASoIaF from this point on). It's currently five books long, and apparently spawned a TV adaptation. Anybody watching that? Is it still on?
Anyway, Gerion is one of Tywin Lannister's brothers, and uncle to Jaime, Cersei, and Tyrion Lannister. The reason he never shows up in person is that by the time the story starts, he's been missing for several years, presumed dead.
Plausible, sure. But not nearly as exciting as the possibility that he somehow slipped into another dimension, became a powerful wizard, and founded a magical boarding school in Scotland.
First, the evidence. The thought actually occurred to me because I was thinking about the similarities between the sigils for Houses Lannister and Gryffindor. Both are represented by a golden lion, rampant, on a crimson field. This initially made me think, Hey, wouldn't it be funny if Godric were a Lannister?
And then I remembered the Sword of Gryffindor, and that's when the whole theory fell into place.
See, Gerion Lannister disappeared after he sailed east (more than a decade before the beginning of Game of Thrones) on a quest to the lost kingdom of Valyria, searching for old family treasures... including the legendary Lannister sword, Brightroar. This sword was forged from Valyrian steel, a metal made with magic which makes it extremely strong and sharp. The Sword of Gryffindor, Godric's legendary blade, was similarly spell-forged and known for its extraordinary qualities. It also has rubies in its hilt, which is a decidedly Lannister flourish (as evidenced by the two Lannister swords fashioned from the late Ned Stark's Ice, Widow's Wail and Oathkeeper)
It occurred to me that Brightroar and the Sword of Gryffindor could very well be the same sword. Which meant that Godric could be Gerion, or at least a descendant. At the time of this revelation, I simply tweeted frantically about it and then went to work and pretended to be an adult. But subsequent combing of the Harry Potter and ASoIaF wikis have revealed even more similarities.
Godric is described as having pale skin and green eyes, both Lannister traits. Of course, Godric had red hair while Lannisters are pretty consistently blond, although that could be easily changed with a spell, Polyjuice potion, or, uh... dye.
Gerion is remembered for his humor and intelligence, and both Jaime and Tyrion considered him their favorite uncle. He gave Tyrion books and encouraged his love of learning, so it's not a huge stretch to imagine him eventually being concerned with education on a larger scale. While Godric is never described as being a barrel of laughs, he is brave (his most prominent trait, in fact) and Gerion was certainly that. For those unfamiliar with the backstory of ASoIaF, Valyria was once a powerful empire that was destroyed thousands of years ago by an unpleasant-sounding event called the Doom. The city of Valyria was abandoned and is avoided at all costs (sailor lore claims that even catching sight of the coastline will lead to an untimely death). When Gerion announced his intention to sail into the ominously-named Smoking Sea (a hellish stretch of water around Valyria bristling with volcanoes and purportedly haunted by demons and krakens), half of his crew abandoned him. But he went ahead with the journey anyway - you don't do that unless you're pretty brave, and at least a little reckless.
Finally, Godric settled in Godric's Hollow, a village in the West Country of England. Gerion was from Casterly Rock, in the Westerlands of the Seven Kingdoms. So, yeah. Pretty much rock solid evidence.
Of course, the natural question that arises here is How would this even be possible? These are characters from totally different series, totally different universes. Gerion might have been searching for a magical sword, but he himself was a pretty ordinary dude. Godric was a powerful wizard, renowned for his wisdom and skill as a wand duelist. Where's the link?
Here's what I think: Gerion did sail into the Smoking Sea, and eventually arrived on the coasts of Old Valyria. His crew slowly died, from a mix of supernatural horrors and (because this is GRRM) probably infections and other ignoble shit, but he eventually reaches the ruined city itself. Gerion finds Brightroar (still clutched in the bony fist of the long-dead King Tommen II), but without any means of leaving Valyria, decides to stick around a little bit and explore. Valyria was once a place of great magic, and Gerion begins to teach himself magic from the remaining lore he can find, probably in an attempt to find a way off and to survive on his surely-dwindling supplies.
But Valyria after the Doom is no ordinary place - it's a corner of the world where reality softens and fades. There are suggestions of other such places existing in the world of ASoIaF, like the Shadow Lands beyond Asshai. This is where the first dragons allegedly came from. And in a GRRM-penned short story about Jaime and Tyrion trying to figure out how to defeat Cthulhu (which, yes, is a real thing), copies of books by Abdul Alhazared of H.P. Lovecraft's Cthulhu Mythos are said to come from the Shadow Lands. That's not the only reference to Lovecraft, by the way. Maps of Essos include references to Ib, Sarnath, K'Dath (Kadath), and Carcosa, all otherworldly place names in Lovecraft's works. And the ironborn's Drowned God bears more than a passing similarity to Great Cthulhu himself.
It might sound like I'm getting off topic, here, but not really: the Lovecraft references are the link that makes the Gerion/Godric theory possible. Lovecraft's "weird horror" stories are all about different dimensions rubbing up against each other and bleeding together. Usually the result of this interchange is that horrific immortal monster-gods breach the membrane of our reality and eat us. Fun stuff. Let's suppose for a moment that some of those monster-gods actually once existed in the dark, distant past of Westeros, and that the Carcosa, Sarnath, and Kadath on those maps are the same ones referenced in Lovecraft's canon. That means that there's a history of dimensional crossover between the ASoIaF universe and Lovecraft's version of ours. It's not too much of a stretch to imagine similar crossover happening with another universe, in this case the one that's home to the Harry Potter stories.[1]
Anyway, long story short: In Old Valyria, Gerion -- either intentionally or by accident -- slides through a crack in his reality and ends up in another.
He arrives in 10th Century England, a society in some ways similar to (and in other ways less advanced than) his own. But one major difference (aside from the spelling of "sir," which must have been really tough for him to deal with for a while) was that magic was very prevalent in this world, with witches and wizards forming a vibrant shadow community alongside the non-magically-inclined Muggles. With the magical knowledge he picked up in Valyria, Gerion naturally falls in with the wizarding community.
Wary about revealing the existence of his largely magic-less world to a bunch of powerful sorcerers, he decides to create a new identity to avoid any awkward questions. Since a few people had met him when he first arrived, he decides to differentiate himself from that golden-haired stranger by dying his hair and growing a beard. He claims to be from a village so small that, a few decades later, everybody's totally cool with renaming it.
He continues to study magic, and finds that he has a real aptitude for it. A true Lannister, he particularly excels at fighting and becomes a famed duelist. Unfortunately, he is unsuccessful in finding a way to return to Westeros, and eventually he resigns himself to the fact that he's stuck in the Harry Potter world for good. Over time he sobers, going from the brash young man who sailed off in search of adventure to a wizard respected for his wisdom and courage. And when someone asks if his magic sword is goblin-made, he says, "Uh... yeah, totally. Goblins." The goblins don't deny this rumor when they hear it, because it's good for business and (later on) it allows them to lay claim to it.
Gerion, now Godric, hooks up with three other famous wizards, and the four of them decide to establish a school to give magical instruction more structure (preceding the European university system by two centuries, by the way). When they decide to break the school up into four Houses, he uses his old coat of arms as their symbol (though he has trouble getting "A Gryffindor always pays his debts" started. Eventually the other founders get so sick of hearing him say it that they forbid him to use the phrase again. It was basically his "fetch"). He gets especially close to Salazar Slytherin, whose cunning and ambition must have reminded him of his family. Things go south, of course, when Slytherin tries to convince the other founders to stop accepting Muggle-born students into the school. Gerion/Godric, who gained all of his magical ability from study rather than genetics, strongly opposes this plan, leading to a rift.
Eventually, Godric dies, far from home but having made a lasting impact on his adopted world. It's also possible, based on a sarcastic comment by J.K. Rowling, that he's actually still alive and is the giant squid in the Hogwarts lake. Which, based on what I've discussed previously, could be a jumping-off point for a further theory that Gerion Lannister is both Godric Gryffindor and a second cousin to Cthulhu.
But that would just be crazy.
[1] Also, both the Cthulhu mythos and the Harry Potter stories (albeit in a dramatically-reimagined form) exist in the sprawling universe of Alan Moore's League of Extraordinary Gentlemen series. While it would be a much more direct connection to just say that Gerion goes there, the LoEG and Harry Potter universes should be seen as definitely separate. Mostly because in LoEG, Harry Potter is a moonchild/anti-Christ who kills Allan Quartermain with penis lightening and then gets turned into sidewalk chalk by Mary Poppins. This is a literal description of what happens in League of Extraordinary Gentlemen: Century: 2009. Alan Moore is a weird dude. Spoiler alert, I guess.
