What's wrong with Robespierre?
He represents perfectly what could be considered the most important era in French history, is historically relevant, has never been used as a leader so far (if that counts for anything), and has a very distinct personality, which could make him a very interesting character to deal with.
I know he doesn't exactly represent the best of France's legacy considering the bloodbath that the French Revolution turned out to be, that his whole God complex is a bit off-putting, and that Civs don't usually have "bad" leaders representing them, but if Portugal can have Maria I and the Aztecs Montezuma, why couldn't France have Robespierre?