Klas Magnus Rosén is a Swedish musician, born 1963 in Gothenburg, and was the bassist of Swedish band HammerFall.
Magnus Rosén started to play the bass when he was 15 years old. When he had played bass for three years he went on his first tour with the band Kung Sune. After the tour he moved to Los Angeles. He became a member in the Swedish heavy metal band HammerFall in 1997.