The Joker was one of the deadly pawns used by the Celestial Toymaker against Steven Taylor and Dodo Chaplet when they were trapped in his realm. When not in a contest, the Joker stayed in playing card form.
Cyril, the Knave of Hearts, often tormented the Joker. The King and Queen of Hearts tried to get the Joker to sit in one of the deadly chairs, but he got suspicious and ran away. (TV: The Celestial Toymaker)