God the Eternal Father.
["We were begotten by our Father in Heaven; the person of our Father in Heaven was begotten on a previous heavenly world by His Father; and again, He was begotten by a still more ancient Father; and so on, from generation to generation, ... we wonder in our minds, how far back the genealogy extends, and how the first world was formed, and the first father was begotten" (Mormon leader, Orson Pratt, The Seer, p.132).
"Some people are troubled over the statements of the Prophet Joseph Smith.... The matter that seems such a mystery is the statement that our Father in heaven at one time passed through a life and death and is an exalted man. This is one of the mysteries.... The Prophet taught that our Father had a Father and so on. Is not this a reasonable thought, especially when we remember that the promises are made to us that we may become like him?" (Mormon leader, Joseph Fielding Smith, Doctrines of Salvation, vol. 1, pp.10, 12).