[7][8][1][9] Hafþór has also appeared on television as an actor, portraying "The Mountain" Ser Gregor Clegane in the HBO series Game of Thrones for five seasons.
He received his primary education at Grundaskóli and then Hjallaskóli hill school, but due to high levels of energy as a child, he had difficulty sitting in a classroom or concentrating on his studies.
[13] As a student at the polytechnic school in Breiðholt,[citation needed] he was enthusiastic about sports and played soccer and did gymnastics, before discovering his passion for basketball in eighth grade.
[15] A lanky teenager, Hafþór gained size and strength through daily exercise, combining basic movements (push-ups, chin-ups, and sit-ups) with working at his grandfather's farm during summers and lifting natural stones in the wilderness.
[21] The following season, he transferred to FSu Selfoss, but after about ten games, it was discovered that he had been playing with a broken bone in his ankle and required surgery.
[24] To commence the 2007–2008 season, Hafþór moved back to play for FSu Selfoss and averaged 6.7 points per game,[25] helping the team to achieve a promotion to the Úrvalsdeild.
[26] However, the troublesome ankle continued and ultimately forced him to retire from basketball at the age of nineteen, shattering his dream of making it to the NBA one day.
[36] One day, when four-time World's Strongest Man champion Magnús Ver Magnússon spotted the twenty-year-old, 6 ft 9 in, 140 kg (309 lb) Hafþór deadlifting in his gym, "Jakaból", he immediately realized his potential as a good prospect for strongman,[37] which paved the way for Hafþór to train with Stefán Sölvi Pétursson, Benedikt Magnússon, Páll Logason, and Ari Gunnarsson.
The following year, while training at the "Strongman Base" gym, Hafþór was nicknamed Ljónið (the Lion) by Stefán Sölvi Pétursson,[38] because he continuously grew bigger and got stronger, eventually reaching his heaviest body weight ever, of 210 kg (463 lb), in 2012.
[53] In his attempt to defend the title in 2019, Hafþór suffered a torn plantar fascia during the group stages and emerged in third place overall, behind Martins Licis and Mateusz Kieliszkowski,[54] thus achieving the longest continuous podium streak in World's Strongest Man history, with eight (2012–2019).
[61][62] Hafþór successfully defended his title at the 2019 Arnold Strongman Classic in dominant fashion and improved on his elephant bar deadlift world record, increasing it to 474.5 kg (1,046 lb) in only his second attempt out of the three allowed.
[63][64] After successfully defending his crown again in 2020, Hafþór became only the second person in history to win the Arnold Strongman Classic three times in a row, after Žydrūnas Savickas.
[65] Following a three-year hiatus due to boxing and powerlifting, Hafþór returned to the 2024 Arnold Strongman Classic and deadlifted 456 kg (1,005 lb) to win the inaugural event.
[71] In 2022, Hafþór made a guest appearance at the 2022 Rogue Invitational in Austin, Texas, and broke the 25.5 kg (56 lb) Highland games one-arm weight over bar world record for the twelfth time, with a clearance of 6.17 metres (20 ft 3 in).
After a two-and-a-half-year hiatus from strength training, Hafþór competed in 2022 Thor's Powerlifting Meet in December and totaled 970 kg (2,140 lb) raw.
[79] Then on 13 February 2023, Hafþór proceeded to officially announce his return to strength sports, stating he will attempt to break the all-time powerlifting total world record at the end of the year.
[6] Even though he was noted primarily for his strength in the moving events during the initial years of his career (for example, medleys and loading races, keg-tossing, power stairs, vehicle pulls, and natural stones, which require good stamina and athleticism), Hafþór kept on improving and upscaled his brute strength, which helped him excel in static events, such as deadlifts, squats, log presses, axle presses, circus dumbbells, etc.
Experts consider the three years from that point onwards as the "highest peak performance" of any strongman in history, due to Hafþór's dominance and having no weaknesses at any event.
Hafþór's international accolades and winning everything there is in the sport cemented his legacy as one of the greatest strongmen of all time,[2] and due to breaking 100+ world records in various static lifts and feats displaying brute strength, many analysts and strongman experts regard him as "the strongest man to have ever walked the earth".
[108] Despite having no boxing experience whatsoever, Hafþór learned the fundamentals of the sport and made commendable progress[109] under the guidance of his coaches, Billy Nelson[110] and Vilhjálmur Hernandez, and support from his two main sparring partners, Skúli Ármansson and Bill Hodgson.
[115][116] On 19 March 2022, after almost two years since its announcement, Hafþór and Hall finally faced each other in Dubai in a fight taglined The Heaviest Boxing Match in History.
Hall started the first round with continuous haymakers, but Hafþór kept his composure and stuck to the basics, focusing on a solid jab and better footwork.
[123] In the same year, he also played Big John in the film Operation Ragnarok, about a town in the south of Sweden isolated after a viral outbreak and the trapped Swedes and immigrants uniting to survive an onslaught.
[125] In 2022, Hafþór had a minor role as Thorfinnr the Tooth-Gnasher in the historical epic fantasy The Northman, which starred Alexander Skarsgård, Nicole Kidman, Ethan Hawke, Claes Bang, Anya Taylor-Joy, and Willem Dafoe.
[129] Hafþór has been accused by several ex-girlfriends of domestic violence,[130][131] including Thelma Björk Steimann[132] (the mother of his daughter), who feared for her life once during a vacation.
[139][140] In late 2017, Hafþór began dating Canadian fitness model Kelsey Morgan Henson, whom he met in Alberta during a promotional event for Icelandic Mountain Vodka and touring for the Warwick Strongman Festival.
[159] Together with Unnar Helgi Danielsson, Dylan Sprouse, and Terry Crews, Hafþór is also a co-founder and brand ambassador of Thor's Skyr, a traditional Icelandic high-protein cultured dairy product high in probiotics and low in sugar.