Who is God?

Christianity

There is one God; as he himself has declared.  He is a thoroughly wondrous entity beyond human understanding, unlimited by the physical laws he created, without beginning or end.  There was nothing but him before creation.  As depicted at Christ's baptism, he is three - in - one; Father, Son and Holy Ghost.

Mormonism

God was once like us, a sinful human on a different world.  As such he had a beginning as a conceived spirit child of that world's god father and one of his god wives.  Yet Mormonism states that there is only one God.  It attempts to erase the obvious paradox by saying that there is only one god of this world.  Mormonism also teaches that Christ and the Holy Ghost are gods in their own right but Mormon authorities vehemently deny the concept of a three - in - one trinity.  Instead they say Father, Son, and Spirit make up one godhead.  Yet women can also become gods and the god of this world has one or more god wives with whom he conceives spirit children.  Mormons believe there are an infinite number of gods and goddesses of other worlds/universes.  However, in the end, they only really see Heavenly Father as their one God.

Notes

While Mormon's paradoxical teachings about "one god" give Christians great discomfort; the same is not true for Mormons.  They hardily accept these paradoxes - making the nature a God a largely unfruitful witnessing topic.  "Who is God?" is not one of the stress areas of Mormonism.