Creator and co-star of the Icelandic-American children's show LazyTown. He was also a noted gymnast.
He was the Icelandic Men's Individual Champion in aerobic gymnastics in 1992, then the Scandinavian champion in 1994 and the European champion in 1994 and 1995.
His LazyTown series aired on Nickelodeon and Nick Jr. in the United States, while Turner Broadcasting System Europe acquired the rights for the U.K.
His wife Ragnheiður Melsteð became the executive producer and co-founder of LazyTown Entertainment. They had two children together.
Stefan Karl Stefansson played Robbie Rotten, one of the villains on LazyTown.