White God is a fae term used to refer to the God of the monotheistic faiths. They consider Him a powerful force and described in terms much like he is in the Bible. He is served by angels, including the four archangels: Uriel, Michael, Raphael, and Gabriel. Lesser angels include messenger angels, guardian angels, and angels of death. At one point a group of angels led by Lucifer rebelled and were cast out. Thirty fallen angels were imprisoned in thirty silver coins that later evolved into the Order of the Blackened Denarius.
The White God is the same deity that serves as patron for the Knights of the Cross, often arranging for random events to favor them, sending them on their missions, and selecting knights. In Grave Peril, for instance, Father Forthill's car broke down only a block from Michael Carpenter's house when the Knight needed a babysitter so that he might go rescue his wife from the Nightmare.
Harry Dresden has stated that he accepts the existence and power of the White God, but does not believe that he himself is, or would be, a proper devoted follower. He always says no to Michael Carpenter's suggestions that he attend church.