Anselm was an Italian monk, an abbot, a philosopher and theologian of the Catholic Church. He was Archbishop of Canterbury from 1093 to 1109.
In this video from Reasonable Faith, Anselm's Ontological Argument is presented. Anselm of Canterbury wrote that God is "that than which nothing greater can be conceived", and believed that if it's possible that a 'maximally great' being exists, then that being must exist. See what you think.