Mormons teach that God the Father was once a man like us.
1 God Was Once a Man
As We Are Now
....
The Prophet Joseph Smith said:
“...It is the first principle of the Gospel to know for a certainty the Character of God, and to know that we may converse with him as one man converses with another, and that he was once a man like us; yea, that God himself, the Father of us all, dwelt on an earth” (Teachings, pp. 345-46; italics in original).
President Brigham Young elaborated on this concept: “It must be that God knows something about temporal things, and has a body and been on an earth; were it not so He would not know how to judge men righteously, according to the temptations and sins they have had to contend with” (as cited by Harold B. Lee, in Conference Report, Apr. 1969, p. 130; or Improvement Era, June 1969, p. 104)...
2 Our Father Advanced and
Progressed Until He Became God (p. 152-153)
President Joseph Fielding Smith said: “Our Father in heaven, according to the Prophet, had a Father, and since there has been a condition of this kind through all eternity, each Father had a Father” (Doctrines of Salvation, 2:47).
President Joseph F. Smith taught: “I know that God is a being with body, parts and passions.... Man was born of woman; Christ, the Savior, was born of woman; and God, the Father was born of woman” (Church News, 19 Sept. 1936, p. 2).
President Wilford Woodruff explained: “[God] has had his endowments a great many years ago. He has ascended to his thrones, principalities and powers in the eternities. We are his children.....We are here to fill a probation and receive an education” (Deseret News Weekly, 28 Sept. 1881, p. 546).
How does it help us to know that the basic elements of God’s life in a mortal world were the same as ours? President Brigham Young explained:
“He is our Father—the Father of our Spirits—and was once a man in mortal flesh as we are....
“...There never was a time when there were not Gods and worlds and when men were not passing through the same ordeals that we are now passing through....
“It appears ridiculous to the world, under their darkened and erroneous traditions, that God has been a finite being” (Deseret News, 16 Nov. 1859, p. 290).
(Search These Commandments, Melchizedek Priesthood Personal Study Guide, Copyright 1984, The Church of Jesus Christ of Latter-day Saints, pp. 152-153)
From THE KING FOLLETT SERMON (Ensign, April 1971):
These ideas are incomprehensible to some, but they are simple. It is the first principle of the gospel to know for a certainty the character of God, and to know that we may converse with Him as one man converses with another, and that 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; and I will show it from the Bible.
Eternal Life to Know God and Jesus Christ
I wish I was in a suitable place to tell it, and that I had the trump of an archangel, so that I could tell the story in such a manner that persecution would cease forever. What did Jesus say? (Mark it, Elder Rigdon!) The scriptures inform us that Jesus said, as the Father hath power in himself, even so hath the Son power—to do what? Why, what the Father did. The answer is obvious—in a manner to lay down his body and take it up again. Jesus, what are you going to do? To lay down my life as my Father did, and take it up again. Do you believe it? If you do not believe it you do not believe the Bible. The scriptures say it, and I defy all the learning and wisdom and all the combined powers of earth and hell together to refute it.
Here, then, is eternal life—to know the only wise and true God; and you have got to learn how to be gods yourselves, and to be kings and priests to God, the same as all gods have done before you, namely, by going from one small degree to another, and from a small capacity to a great one; from grace to grace, from exaltation to exaltation, until you attain to the resurrection of the dead, and are able to dwell in everlasting burnings, and to sit in glory, as do those who sit enthroned in everlasting power. And I want you to know that God, in the last days, while certain individuals are proclaiming His name, is not trifling with you or me.
The King Follett Sermon