Marozia of Tusculum was the closest thing we had to a female pope. Pope Joan was probably a myth, but we can be sure Marozia existed, since she was related to seven popes.
Marozia: The De Facto Ruler of the Papacy

Marozia of Tusculum was the closest thing we had to a female pope. Pope Joan was probably a myth, but we can be sure Marozia existed, since she was related to seven popes.