|Occupation||Uncle and Advisor of King Gerard|
|First Appearance||Season 2, "Return Of The Clockwork Smurf"|
Sir Leopold is the evil uncle of King Gerard. He only appears in the Johan And Peewit episode "Return Of The Clockwork Smurf", in which he schemes to get Clockwork Smurf out of the way so that he can control his naïve young nephew, who depends totally on his trusted mechanical friend's advice in ruling his kingdom. After secretly sabotaging Clockwork so that he is unable to function, he exploits his grief-stricken nephew's distraction to become the power behind the throne, turning the erstwhile happy kingdom into an unhappy dictatorship in which taxes are raised unreasonably high, programs to help the poor are cut, and children are forced to work. Unfortunately for Sir Leopold, Sir Johan, Peewit, and Princess Savina, who is a cousin of Gerard's, come to visit and immediately start noticing that something is wrong. Despite his efforts to throw them off, they eventually discover what he has been up to, so he traps them and Gerard along with Dame Barbara in a dungeon cell, which he then floods to drown them. However, Gerard learns to think on his own thanks to Johan's advice, and stages an escape just in time. Then with the help of his friends, including the Smurfs along with a revived Clockwork, courtesy of Handy Smurf, he gets the goods on his evil uncle and restores his kingdom to its happier state.
There is no mention of Leopold's exact relations to Lady Imperia, although if she was Gerard's aunt, he was very possibly her brother or brother-in-law, depending on which side of Gerard's family he comes from.