Leo X

Pope Leo X (11 December 1475 – 1 December 1521), born Giovanni di Lorenzo de' Medici, was the Pope from 1513 to his death in 1521.

Leo X was an ally of the Assassin Order, through his father Lorenzo de' Medici, who was rescued by the Assassin Ezio Auditore da Firenze during the Pazzi Conspiracy in 1478. Leo X's ascendance as Pope reassured the Assassins that their presence in Rome would continue to thrive.

Source

 * Assassin's Creed: Revelations novel