Question: who is the actor that plays robbie rotten
Answer: Stefán Karl Stefánsson ( / ˈstɛfən ˈstɛfənsən / ; Icelandic : ( ˈstɛːvaun ˈkhartl̥ ˈstɛːvaunsɔn ) ; born 10 July 1975 ) is an Icelandic actor , best known for playing the villain Robbie Rotten on the children 's television series LazyTown .