Who is Anastasius from Pope Joan and what is their importance?

Anastasius is the treacherous son of Arsenius who tries for years to become Pope. Anastasius is forced to watch his uncle's assassination as a child, which affects him for the rest of his life. Anastasius is responsible for the fire that burns the Borgo and other deceptions, including the deaths of Gerold and Joan. He never becomes Pope but becomes known for his written history of the papacy which, interestingly, does not include the papacy of John Anglicus until it is modified much later.