You know that feeling when you're watching a show and suddenly a character looks... different? It's jarring. Most shows try to hide it with a new haircut or a "long journey" away from the screen. Game of Thrones didn't even bother. They just swapped out the most terrifying man in Westeros three separate times.
If you’re wondering who plays the mountain, the answer depends entirely on which season you’re binge-watching. It’s not just one guy. It’s a trio of giants who each brought a totally different vibe to Ser Gregor Clegane. Honestly, the evolution of the character from a literal "Mountain" of a man to a silent, undead zombie is one of the weirdest casting journeys in modern TV history.
The Mountain is a nightmare. He’s the guy who burned his brother’s face over a toy. He’s the guy who—well, we all remember the Oberyn Martell incident. But finding a human being who actually fits the description in George R.R. Martin’s books is nearly impossible. In the novels, Gregor is closer to eight feet tall. Finding actors who are that big and can actually move (or act) is a nightmare for casting directors like Nina Gold.
The First Mountain: Conan Stevens
In Season 1, the role belonged to Conan Stevens. He’s an Australian actor and former wrestler who stands about 7' tall. You probably remember him best from the tournament scene where he gets angry and decapitates a horse with a single swing of a broadsword. It was brutal.
Stevens actually looked like a knight. He had the build of a professional athlete and a face that felt genuinely mean. Fans generally loved him because he felt like a physical threat that could actually happen in the real world. So, why did he leave? It wasn't drama. It was The Hobbit. Stevens landed the role of Bolg in Peter Jackson’s trilogy and had to choose between being a secondary villain in a new HBO show or a primary villain in a massive film franchise. He chose the movies. Ironically, his role in The Hobbit ended up being mostly CGI, while Game of Thrones became the biggest thing on the planet. Talk about a tough break.
Ian Whyte: The Tallest of the Bunch
When Season 2 rolled around, the production needed a replacement fast. They turned to Ian Whyte. If you’re a die-hard fan, you’ve seen Ian Whyte’s face (and body) a dozen times on the show. He’s a 7'1" Welsh actor and former basketball player who has played White Walkers, giants (including Wun Wun), and, for a brief window, Ser Gregor Clegane.
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But here’s the thing: Whyte’s Mountain felt... off. He was incredibly tall, but he was lanky. He didn't have that "I can crush a skull with my thumb" bulk that the character required. During the Harrenhal scenes, he felt more like a very tall, very tired soldier than a force of nature. It’s no disrespect to Whyte; he’s a legend in the "creature acting" world. But as the Mountain, he lacked the sheer mass. The showrunners clearly realized they needed someone who looked like they ate other knights for breakfast.
Hafþór Júlíus Björnsson: The Definitive Ser Gregor
Then came Season 4. Everything changed. The show entered its most iconic era, and they found the man who would define the role until the very end: Hafþór Júlíus Björnsson.
Björnsson, an Icelandic strongman, didn't just play a strong man. He was the World's Strongest Man. Literally. He won the title in 2018. When he showed up for the trial by combat against Oberyn Martell, the audience finally understood the name. He was a slab of muscle.
Interestingly, Björnsson was actually shorter than Ian Whyte, standing at 6'9". But he weighed nearly 400 pounds of pure Icelandic power. When he stood next to Pedro Pascal (Oberyn), the scale was terrifying. You didn't need special effects to believe he was dangerous. You just needed to look at his arms.
The Training Regimen of a Giant
To keep that physique, Björnsson wasn't just hitting the gym. He was consuming roughly 10,000 calories a day. Imagine eating a steak every two hours. It sounds like a dream until you realize you have to wake up in the middle of the night just to shove more protein down your throat so your body doesn't start burning its own muscle for fuel.
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He once famously stated that he had to eat constantly to maintain his weight for the role. This wasn't "Hollywood fit." This was "World Record Powerlifter" fit. During his tenure as who plays the mountain, the character shifted from a speaking role to a silent, hulking bodyguard for Cersei Lannister. This worked perfectly. Björnsson’s physical presence did all the talking.
From Human to "Robert Strong"
After the duel with Oberyn, the Mountain "dies," but Qyburn brings him back using some dark, pseudo-science alchemy. From Season 5 onwards, Björnsson spent hours in the makeup chair. His skin was turned a sickly shade of purple and blue. His eyes were bloodshot.
The makeup artists actually did such a good job that Björnsson looked legitimately horrifying even when the cameras weren't rolling. There’s a famous story where he went to a local shop in Belfast still in his "zombie" makeup, and the cashier nearly had a heart attack.
The Reality of Casting Giants
Finding people of this size is a logistical nightmare for a production. Everything has to be custom-made.
- Armor: You can't just rent a suit of plate mail for a 6'9" strongman. Every piece of Gregor’s armor was forged specifically for the actor’s dimensions.
- Stunt Doubles: How do you find a stunt double for the World's Strongest Man? You don't. Björnsson did a significant amount of his own physical work, though the more dangerous horse stunts often required creative camera angles.
- Perspective: Directors often used "forced perspective" to make the actors look even bigger. This involves placing the actor closer to the camera and the other performers further back. However, with Björnsson, they barely had to do it. He naturally towered over the rest of the cast.
Why the Constant Recasting Matters
In most shows, recasting a major character kills the immersion. Think about the outcry when The Witcher swapped Henry Cavill for Liam Hemsworth. So why did Game of Thrones get away with it?
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Part of it is the helmet. For a large portion of the early seasons, the Mountain is encased in steel. You see the size, not the face. By the time the face became iconic, Björnsson had the job.
But also, the Mountain isn't really a "character" in the traditional sense. He's a walking disaster. He represents the sheer, unthinking cruelty of the Lannister regime. Whether it was Conan Stevens' aggressive energy or Björnsson’s silent menace, the function of the character remained the same: be the biggest, scariest thing in the room.
The Final Showdown: Cleganeball
For years, fans begged for "Cleganeball"—the final fight between Sandor (The Hound) and Gregor (The Mountain). When it finally happened in the penultimate episode of the series, Björnsson had been playing the role for five seasons. He had become the character.
The fight took place on a crumbling staircase in King's Landing while a dragon leveled the city around them. It was poetic. The two brothers, both products of extreme violence, finally ended each other. It’s worth noting that Björnsson and Rory McCann (who played the Hound) actually became quite close during filming. Despite the onscreen hatred, they spent a lot of time discussing training and diet. McCann is a big guy himself—about 6'6"—but even he looked small next to the Icelandic giant.
Key Takeaways for Fans
If you're tracking the history of Ser Gregor, keep these points in mind:
- Check the Season: If it’s Season 1, it’s Conan Stevens. Season 2? Ian Whyte. Seasons 4 through 8? Hafþór Júlíus Björnsson.
- Look at the Build: If the Mountain looks oddly skinny, you're likely watching the Harrenhal arc in Season 2.
- Appreciate the Craft: Behind that helmet was a rotating door of some of the most physically impressive men on the planet.
The legacy of who plays the mountain is ultimately one of physical transformation. While the show had many brilliant actors, the Mountain required something else: presence. Björnsson provided that in spades, turning a secondary villain into a cultural icon that continues to haunt the nightmares of anyone who hates the sound of crunching bone.
To truly understand the scale, you should watch the behind-the-scenes footage of the Season 4 duel. Seeing Björnsson swing a real greatsword—even a blunted one—shows the terrifying reality of what that kind of strength looks like in person. He wasn't just acting; he was moving weight that would pin a normal person to the ground.
Next Steps for the Curious
- Follow the Strongman Circuit: If you want to see what the final Mountain is up to now, check out Björnsson's boxing matches or his recent return to powerlifting. He lost a massive amount of weight to box, then put it back on to break more records.
- Compare the Footage: Go back and watch the Season 1 tournament scene followed by the Season 4 trial by combat. The difference in movement style between Stevens and Björnsson is a fascinating study in how different bodies handle "heavy" roles.
- Read the Books: To see just how much more monstrous the literary version is, pick up A Song of Ice and Fire. You'll realize that as big as these actors were, they were still smaller than the Gregor Clegane of George R.R. Martin’s imagination.