Shrimad Bhagavad Gita As It Is -Shri Shrimad A.C Bhaktivedanta Swami Prabhupada
Chapter 4: Verse-1
In this millennium, the sun-god is known as Vivasvän, the king of the sun, which is the origin of all planets within the solar system. In the Brahma-samhitä  it is stated:
“Let me worship,” Lord Brahmä said, “the Supreme Personality of Godhead, Govinda [Krsna], who is the original person and under whose order the sun, which is the king of all planets, is assuming immense power and heat. The sun represents the eye of the Lord and traverses its orbit in obedience to His order.”
The sun is the king of the planets, and the sun-god (at present of the name Vivasvän) rules the sun planet, which is controlling all other planets by supplying heat and light. He is rotating under the order of Krsna, and Lord Krsna originally made Vivasvän His first disciple to understand the science of Bhagavad-gita. The Gita is not, therefore, a speculative treatise for the insignificant mundane scholar but is a standard book of knowledge coming down from time immemorial. In the Mahäbhärata  we can trace out the history of the Gita as follows:
tretä-yugädau ca tato
“In the beginning of the millennium known as Tretä-yuga this science of the relationship with the Supreme was delivered by Vivasvän to Manu. Manu, being the father of mankind, gave it to his son Mahäräja Iksväku, the king of this earth planet and forefather of the Raghu dynasty, in which Lord Rämacandra appeared.” Therefore, Bhagavad-gita existed in human society from the time of Mahäräja Iksväku.
- Sänti-parva 348.51–52