“It’s my passion and my dream to become the world’s strongest man,” said Hafthor Julius Bjornsson, the Icelandic giant best known as Gregor Clegane, or the Mountain, on HBO’s “Game of Thrones,” which returns this month.

This isn’t a figurative statement: The World’s Strongest Man is an annual competition — perhaps you have seen those taking part in the act of pulling airplanes or racing while carrying pairs of refrigerators. On three occasions, Mr. Bjornsson, who stands 6 feet 9 inches and weighs 396 pounds, has made the top three.

Over the last seven years, he has added 166 pounds to his frame by ditching most of his cardio workouts, eating like a horse and lifting weights.

The Man Hafthor Julius Bjornsson, 27, also known as Thor. Actor, strength competitor, father and boyfriend. (“My girlfriend, she’s a bit small,” he said. “She’s around 163 pounds.”)

The Gear Free weights and barbells, a bench press and simple weight machines.

The Uniform He wears spandex shorts, a weight belt and a custom tank top that reads, “Training to Fight the Mountain.” “When I post on my Instagram wearing my tank top, people laugh and say, ‘Aren’t you the Mountain?’ I say, ‘Yes, I am, but I am fighting myself every day to try and be better.’”

The Regimen A series of basic dead lifts, bench presses and squats in sets of three to five, using extreme amounts of weight, for two to four hours every day. Mr. Bjornsson already dominates the carrying and dragging events in the World’s Strongest Man, so his focus is on other things now. “I train mostly for my static power: dead lifts,” he said.

The Trainer Mr. Bjornsson works out at a gym run by Magnus Ver Magnusson, a four-time World’s Strongest Man winner. “To become one of the best stone lifters in the world, you have to have a good trainer,” he said.

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The Goal “I would like to win the World’s Strongest Man competition, as you would win best writer in the world,” he said. “Is that a title that exists?”

The Diet Mr. Bjornsson packs away eight meals a day. Breakfast consists of eight eggs, with oatmeal and fruit. The other meals comprise meats, grains and vegetables as well as fatty foods like avocado and organic peanut butter. “I eat quite healthy for a big guy like me, but you get sick of eating all the time,” he said. “Today, I was supposed to have chicken with sweet potatoes and greens. Because I didn’t want that, I had salmon. We have very good fish in Iceland. Everything is expensive in Iceland, especially food, and especially healthy food.”

The Bonus Round He swims and bikes for cardio. “You can’t just be strong,” he said. “You have to be quick. You have to have flexibility.”

The Log Mr. Bjornsson broke a 1,000-year-old record, legend has it, held previously by a Viking named Orm Storulfsson, by carrying a 1,433-pound, 30-foot-long log over his shoulder for five steps. It is said that Storulfsson lasted three steps — with a 1,410-pound log — before his back broke.