According to the Mormon doctrines, who created the universe?

Your question has an assumption that is not correct; "If the Almighty God began life as a man." Not anywhere in Mormon Doctrine (Canonized Scripture) does it say that God began life as a non-divine man. In fact there are many scriptures that state that God is eternal and has always been God.

The statement that "As man is God once was, and as God is man may become." Does not state that God, when He was a man was not divine and was not still God. Jesus Christ is God, and He was once a man and still is a man, but was always divine and the Son of God.

As man is Christ once was, and as Christ is man may become.

Philippians 3:21; "Who shall change our vile body, that it may be fashioned like unto his glorious body, according to the working whereby he is able even to subdue all things unto himself." The resurrected righteous shall have a glorious body even like Christ body.

Revelation 21:7; "He that overcometh shall inherit all things; and I will be his God, and he shall be my son." If we overcome evil we can inherit all things that the Father hath.

1 Peter 5:6; "Humble yourselves therefore under the mighty hand of God, that he may exalt you in due time:" What else does it mean to be exalted, other than becoming a glorified Son of God? 2 Peter 1:3-4; "According as his divine power hath given unto us all things that pertain unto life and godliness, through the knowledge of him that hath called us to glory and virtue: Whereby are given unto us exceeding great and precious promises: that by these ye might be partakers of the divine nature, having escaped the corruption that is in the world through lust." The righteous shall be given godliness and are partakers of the divine nature, and if divine, then they are gods and Lords, so one can understand that Christ is the God of gods and Lord of Lords, not a God of evil gods or evil Lords. Revelation 19:16, Deuteronomy 10:17.

Revelation 3:21; "To him that overcometh will I grant to sit with me in my throne, even as I also overcame, and am set down with my Father in his throne." If we are joint-heirs with Christ and inherit all things that the Father has, becoming partakers of the divine nature and obtain the glory of our Lord and sit down with Christ in His throne and become one with God, what does that say about the righteous heirs. Those that share all things, Glory, Knowledge, Power and divine nature with the Father are worthy of, according to the word of God, the title “God.”

Every galaxy in the universe is/was created or in motion to pass threw an Eternal Round. Our Galaxy was created by the 1st borne son (Jehovah) of the God we refer to as Heavenly Father or Eloi

Our Milky Way Galaxy and all the billions of Galaxies in the Universe have an exalted man known as the Father who chose the absolute and only intelligent spirit who could become a God while still in the spirit. Each Galaxy is created by the 1st bourn under the direction of the Father. Our earth is the last of Jesus Christ creations. It was to become the earth and is the 2nd estate. Here is where man would be tried and tested.

As you gaze through our galaxy and behold other Galaxies in the Universe know this. These Galaxies all are the dominion of one God and only one God. The number of galaxies and the God who is referred to as 'Father in Heaven' is eternal. Bro Bob Stephens

It is preposterously impossible for mortal humanity to comprehend the immortal eternal wondrous mystery of the omnipotent God and all the visible and invisible manifestation of the universe and all its inhabitants and creation. It is a glorious mystery that has no answer known to mortality and humanity. But at the same time, cannot be denied and repudiated that God is, and that it had to be Him who is outside of the universe commanded the universe or universes and all their inhabitants, things, creatures and components to be created out of nothing by the power of His word of infinite Faith and inconceivable wisdom.

I apologize for dredging up this old question but it contains incorrect information that I thought worth addressing.

The original question contains an unsubstantiated assumption that seems to be shared by those answering.

"If the Almighty God began life as a man, He must have been part of this universe."

This is an assumption and not Mormon doctrine.

Here is what we have on the subject

I am the Beginning and the End, the Almighty God; by mine Only Begotten I created these things; yea, in the beginning I created the heaven, and the earth upon which thou standest.

I took that one from Moses 2. It's mirrorred twice in Genesis. I take it to mean that God created the universe but that's my interpretation. Others take it to mean that God created this earth and the sky; also an interpretation.

I've heard speculation that God created separate universes for each planet He placed His children on (which I thought sounded silly), that each galaxy contains a world with people on it (sounds more plausible but still pure speculation) and several other variants on that theme.

moses 1:31-33

And worlds without number have I created; and I also created them for mine own purpose; and by the Son I created them, which is mine Only Begotten. And the first man of all men have I called Adam, which is many. But only an account of this earth, and the inhabitants thereof, give I unto you. For behold, there are many worlds that have passed away by the word of my power. And there are many that now stand, and innumerable are they unto man; but all things are numbered unto me, for they are mine and I know them.

It's human nature to take the information we are given and make (what seems to us to be) logical deductions and conclusions and then assume that those conclusions are fact. We need to remember where the raw data ends and the interpretation begins.

The scriptures are the raw data and they don't mention the universe by name. They don't tell us about the Almigty God's relationship to anything other than us (Mormons include angels in that 'us'). "Does our Heavenly Father have a father?" Again, the scriptures don't tell us about His relationship to anyone other than us.

Mormons believe that, in general, the universe was created. That there was a creator and that the creation story was handed down by the one true God to Moses.

Beyond that, it is considered a mystery.

Brigham Young once said:

As to the Bible account of the creation we may say that the Lord gave it to Moses. If we understood the process of creation there would be no mystery about it, it would be all reasonable and plain, for there is no mystery except to the ignorant.
John A. Widtsoe, Discourses of Brigham Young _{(Salt Lake City: Deseret Book, 1978, p. 259)}

So, the one true God could not have been the creator of the universe. Exactly who created the universe or how it was created is left as a mystery.

Having said this, it is noted that while God did not create the universe, he did create mankind and the earth. As such, he is still the Creator, just not the creator of the universe.

There is a article regarding the Mormon doctrine of creation, written by James Talmage.