Who is God?

"We believe in God the Eternal Father and in his son, Jesus Christ, and in the Holy Ghost."

-- First Article of Faith, Church of Jesus Christ of Latter-day Saints.

One God in purpose, but three Beings. The Godhead -- a valid, New Testament term.

Or one could imagine drawing a circle around God the Father, God the Son and God the Holy Ghost and labeling God that which is within the circle. Both Latter-day Saints and other Christians can do this without violating their respective beliefs about deity.