In Mormon theology, God was originally a human on another planet, with his own God (like us). He turnedinto God later.
• Milton R. Hunter: “Mormon prophets have continuously taught the sublime truth that God the Eternal Father was once a mortal man who passed through a school of earth life similar to that through which we are now passing. He became God-an exalted being. … He grew in experience and continued to grow until He attained the status of Godhood. In other words, He became a God by absolute obedience…” [The Gospel Throughout The Ages, 104, 114-15.]
Mormonism's Official Curriculum Material etc.
• “When we lived with our Heavenly Father, He explained a plan for our progression. We could become like Him, an exalted being… Joseph Smith taught: ‘[God] was once a man like us… God himself, the Father of us all, dwelt on an earth, the same as Jesus Christ did’” [Gospel Principles (The Church of Jesus Christ of Latter-Day Saints, 2009), 275, 279.] [(cf. Teachings of Joseph Smith, 345.][Also History of the Church, Vol 6, 306.][Also King Follett Sermon, Ensign, April 1971]
• Brigham Young (Mormonism's 2nd president-prophet): “He is our Father—the Father of our spirits, and was once a man in mortal flesh as we are, and is now an exalted Being.” [Journal of Discourses vol. 7:333]
• Joseph Smith (Mormonism's founding president-prophet): “it is necessary that we should understand the character and being of God, and how he came to be so; for I am going to tell you how God came to be God. We have imagined and supposed that God was God from all eternity, I will refute that idea, and will take away and do away the veil, so that you may see. … he was once a man like us; yea, that God himself, the Father of us all, dwelt on an earth, the same as Jesus Christ himself did” [History of the Church, Vol. 6:305-306.] (From the famous King Follett Sermon)
John Widtsoe (Mormon Apostle): “Therefore if the law of progression be accepted, God must have been engaged from the beginning, and must now be engaged in progressive development, and infinite as God is, he must have been less powerful in the past than he is today.” [A Rational Theology, 24.]
• B. H. Roberts (Mormon apostle & church historian): “God the Father was not always God, but came to his present exalted position by degrees of progress as indicated in the teachings of the prophet,” [A New Witnesses for God 1:476]
• Brigham Young (Mormonism's 2nd president-prophet): “the Father, after He had once been in the flesh, and lived as we live, obtained His exaltation, attained to thrones, gained the ascendancy over principalities and powers, and had the knowledge and power to create—to bring forth and organize the elements upon natural principles. This He did after His ascension, or His glory, or His eternity, and was actually classed with the Gods” [Journal of Discourses, vol. 4:217]
• Orson Hyde: “He knows everything. How? When His angels and ministers tell Him of it, like any other ruler.” [Journal of Discourses vol. 2:64]
• Heber C. Kimball (First Presidency Counselor): “God is a natural man… Where did he get his knowledge from? From his Father, just as we get knowledge from our earthly parents.” [Journal of Discourses vol. 8:211]
• George Q. Cannon (First Presidency Counselor): “… advancing as our Father in heaven advances, for there is progress for our father and for our Lord Jesus. There is no such thing as standing still in the eternal work of our God. It is endless progress, progressing from one degree of knowledge to another degree.” [Millennial Star 61:117]
• Wilford Woodruff (Mormonism's 4th president-prophet): “God himself is increasing and progressing in knowledge, power, and dominion, and will do so, worlds without end” [The Discourses of Wilford Woodruff, 3. (As cited here by McKeever)]