The Cosmological Argument
The Cosmological Argument attempts to prove that God exists by showing that there cannot be an infinite number of regressions of causes to things that exist. It states that there must be a final uncaused-cause of all things. This uncaused-cause is asserted to be God.
Thomas Aquinas (1224-1274) had a version of the Cosmological Argument called the Argument from Motion. He stated that things in motion could not have brought themselves into motion but must be caused to move. There cannot be an infinite regression of movers. Therefore, there must be an Unmoved Mover. This Unmoved Mover is God. [Excerpted from an article by matt Slick. Read more here.]