Pope Constantine became Pope on March 25, 708 C.E. Do not confuse Pope Constantine with the Roman Emperor Constantine the Great (ca. 272-337).
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.
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.
He was elected as pope on April 22, 1073.
There has never been a Pope John Benedict.
The pope has always been a Christian.
Vatican City
Pope John XXII became pope on August 7, 1316.
Since Pope Francis is the first and only pope by that name, there is no need for a number after his name. If a pope in the future also decides to take the name Francis, he will become Pope Francis II and then the original Pope Francis will become Pope Francis I.
He was 58 years old when elected as pope.