Pius III

Pius III, born Francesco Todeschini Piccolomini (May 29, 1439 – October 18, 1503), was the Pope that succeeded Alexander VI, after the latter's death by the hands of his son.

Pius III was sixty-four when he was elected to the Papacy, and he was known for his poor health. He only reigned for twenty-six days, after which Julius II succeeded him. During his Papacy, he served neither the Assassins nor the Templars, but he did start the moral reformation of the church to undo some of his predecessor's damage.

Source

 * Assassin's Creed: Brotherhood novel