Stefán Karl Stefánsson is an Icelandic actor, best known for playing the villain Robbie Rotten on the children's television series LazyTown. wikipedia.org
Definition #2 for "robbie rotten"
Robbie Rotten was the primary antagonist in the Nick Jr. children?s television series LazyTown; played by the Icelandic film and stage actor Stefán Karl Stefánsson. The character is known for being a lazy man who constantly schemes to undermine the influence of the protagonists Stephanie and Sportacus.