Stefán Karl's career started in 1994 at the age of 19, when he worked as a puppeteer for television. During his years as a puppeteer, he had also been studying at the Drama Academy of Iceland. However, he was unsatisfied with the perspectives of Icelandic drama standards. He recalled that his principal at his high school said that "acting is not about making faces and changing your face", which he disagreed with. Later, Stefán Karl was invited by
Magnús Scheving, an Icelandic gymnast, to portray one of the characters in the second
LazyTown play. Magnús created the plays due to his concerns about Iceland's younger generation lacking sufficient physical exercise. Stefán Karl explained that "[Magnús] wanted the kids to get healthier, so he created this musical called
LazyTown. He played
Sportacus, the fitness fanatic, and I was
Robbie Rotten, the guy who liked to stay indoors and sleep". After initial success with the musical,
Nickelodeon eventually made a deal with the creators of
LazyTown to air the first 40 episodes of
LazyTown along with a special studio built in Iceland. During the first few years of
LazyTown in the early 2000s, Stefán Karl initially knew no English, but he soon became fluent. ==Personal life ==