I discovered a rather funny medieval figure known as Charles the Simple, who was a notoriously useless French king from the 9th to 10th century. His subjects overthrew him and locked him in a jail because he was such a bad general. “The Simple” is not a wise name for a king to earn. Three centuries later, Simon de Montfort said that Henry III should be locked up like Charles the Simple due to Henry’s own poor military record. Thinking about locking up your king is one thing, but saying it to his face like Simon did is flirting with treason.
Grady P Brown - Author 
Is Simple Simon the same Simon of Simon Says fame? Both seem to relate to your post.
Not to my knowledge. It is just the name of the man who rebelled against King Henry III of England.