Odo was never the pope.
Saladin was never a pope.
Saladin was not a pope.
A priest could only become pope if he is elected by the cardinals in conclave.
To become a pope, one must be at least 18 years old.
You become a pope when you are elected as such in a secret conclave held in the Sistine Chapel of the Vatican to replace a pope who as either died or retired.
There has never been a Pope John Benedict.
He was elected as pope on April 22, 1073.
Vatican City
The pope has always been a Christian.
Pope John XXII became pope on August 7, 1316.
The novel you are referring to is likely "The Agony and the Ecstasy" by Irving Stone, which is a biographical novel about the life of Michelangelo. In the book, Michelangelo is the main character who interacts with Pope Julius II, but he does not become pope himself.