Sven Magnus Øen Carlsen (সোভেন ম্যাগনাস ওন কার্লসেন) is a Norwegian chess grandmaster. Carlsen is a five-time World Chess Champion, five-time World Rapid Chess Champion, and the reigning (shared with Ian Nepomniachtchi) eight-time World Blitz Chess Champion. He has held the No. 1 position in the FIDE world chess rankings since 1 July 2011 and trails only Garry Kasparov in time spent as the highest-rated player in the world, while holding the record for the longest consecutive reign. His peak rating of 2882 is the highest in history. He also holds the record for the longest unbeaten streak at the elite level in classical chess at 125 games.

Carlsen was born in Tønsberg, Norway, on 30 November 1990 to Sigrun Øen (1963–2024), a chemical engineer, and Henrik Albert Carlsen, an IT consultant. The family spent one year in Espoo, Finland, and then in Brussels, Belgium, before returning to Norway in 1998, where they lived in Lommedalen, Bærum. They later moved to Haslum. Carlsen showed an aptitude for intellectual challenges at a young age. At two years, he could solve 50-piece jigsaw puzzles; at four, he enjoyed assembling Lego sets with instructions intended for children aged 10–14.

Carlsen had an aggressive style of play as a youth, and, according to Simen Agdestein, his play was characterised by "a fearless readiness to offer material for activity". As he matured, Carlsen found that this risky playing style was not as well suited against the elite of the chess world. When he started playing in top tournaments, he had trouble getting much out of the opening. To progress, Carlsen's style became more universal, capable of handling all sorts of positions well. He opens with both 1.d4 and 1.e4, as well as 1.c4, and, on occasion, 1.Nf3, thus making it harder for opponents to prepare against him and reducing the effect of computer analysis. He said in 2015 that the middlegame is his favourite part of the game as it comes down to "pure chess".

As of 2016, Carlsen identifies as a social democrat and mostly follows a vegetarian diet; two of his sisters are vegetarians.

Carlsen is an avid football fan, with Real Madrid CF as his favourite club. In recognition of becoming world chess champion, he took the honorary kick-off in a La Liga game between Real Madrid and Real Valladolid on 30 November 2013. Carlsen also follows the Premier League and plays fantasy football. In December 2019, he reached the No. 1 spot on a Fantasy Premier League game, ahead of seven million other players, before eventually finishing the season in 10th place.