<human>:  Who came up with the famous philosophical argument called ‘The Ontological Argument’?
<bot>: The Ontological Argument was first proposed by St. Anselm in the 11th century. It is a valid argument that attempts to prove the existence of God, based on the premise that the concept of God is not self-contradictory. The argument is often used to defend theism, the belief that God exists.