I never thought about it this way, but the traditional God of Christianity, Judaism, and Islam is an atheist.
The Mormon concept of God is quite different. Elohim, the Mormon God, was once a man, who evolved to a "God" status or position. He had a father, who also had a father, going back in an infinite regress of Gods. There is no "prime mover" in Mormonism, which raises all sorts of interesting theological questions.
Mormon leaders have tried to weasel out of this theology recently, but there are too many teachings over the years to simply dismiss. Unfortunately, by eliminating or weakening this belief, Mormon leaders are striking at the foundation of one of their more beautiful doctrines: eternal progression (i.e., there is no limit to human progression, and human beings can become like God). Of course, beauty does not make something true, with all due respect to John Keats' Ode on a Grecian Urn.