Believed to be an all-powerful god by most transformers, Primus is as much a mystery as he is an inspiration. Many stories have appeared over time, such as that he, like Unicron, was one of Primacron's Super Transformer, and eventually became the Planet Cybertron, and that eventually all robotic life on that planet came from his own spark through the super computer Vector Sigma. Is some ways this is supported by the fact that Unicron tasked Starscream with hooking his Head up to the planet so that he would have a new body to control.
However this is greatly disputed among historian bots because of the vision that Rodimus Prime reported seeing when he traveled deep into the Matrix of Leadership, where he learned that it was the Quintesson's that created had created both the Autobot's and the Decepticon's before being driven off the world, thanks in large part to Alpha Trion and his Coda Remote. Eventually historian bots began to look into the possibility that both stories were true, and that the Quintesson's in fact came upon Cybertron at some point after the Primus was constructed and decided to make it, not only their home, but also the base of their robot operations.
If this was what had happened, then it is possible that eventually the Quintesson's learned about Primus, or at least his life-force, and tapped into it with Vector Sigma in order to bring life to their robots. If that is the case then it is also possible that it was Primus that, in some way, helped Alpha Trion to construct the Coda Remote in order to save his "children" from the Quintesson's.
Unfortunately this history, though still mostly valid, is in dispute now by the historian bots due to the Great Reformatting that happened at the end of the Spark Wars, and the discovery that the planet had once supported organic life, similar to what is currently found on the Planet Earth.
Regardless of his origins, It is said that Primus left his children several gifts after the defeat of the Quintesson's. The first was the gift of life through the continued use of Vector Sigma in order to allow new generations of robots to be born. The Second was said to be a link to his vast knowledge, or wisdom, so that those that led his children, or the Primes, would do so with the same wisdom and compassion that he had for all his children. This is said to have been the origin of the Autobot Matrix of Leadership. Finally he left his children a book of his word, or what humans would call predictions for the future of the planet. Which eventually became known as the Covenant of Primus, which was held in such reverence by both the Autobot's and the Decepticon's that both Optimus Prime and Megatron took two of the last copies of it with them when they left Cybertron to find new sources of Energon.
We now know that the following passages from the Covenant actually referred to the Beast Wars that took place on prehistoric Earth. Each passage will be explained after it is given:
"...and a mighty warrior came down from the sky... and a rainbow was on his head... and his feet were as pillars of fire... and the great dragon was cast out upon the Earth... and his followers were cast out with him." This passage refers to the arrival of Tigerhawk into the Beast Wars and how he destroyed the Predacon base.
"...and as it were a great mountain, raging with fire, arose from the sea." Refers to when Megatron resurrected the Decepticon Warship, the Nemesis, from its resting place at the bottom of the ocean, and how it rose from the sea.
"I am alpha and omega. The beginning and the end. I am that which is. Which was, and is yet to come... and you will know my name is Megatron, when I lay my vengeance upon you!" This passages only purpose to explain how much actual power Megatron now had while in control of the Nemesis.
"...and the stone of their protection shall rise up forever and ever, as those who live and war as beasts face their final cycle." Tells how Megatron had the Nemesis's tractor beam tearing apart the mountain in which the Ark was housed.
"...and there came a hero who said: 'Hurt not the Earth, nor the sea, nor the trees, nor the very fabric of time,' but the hero would not prevail...nor would he surrender." This passage tells how Optimus Primal confronted Megatron in one last futile battle to stop him from insane mission.
"In the spark of an enemy, there will be salvation, and in the darkest hour there will be a light." This final passage tells how the clone of Dinobot helped the Maximal's to defeat Megatron and the Nemesis, as well as give them a way to return home.
How Primus knew these events would happen is unknown, just as it will never be truly known if he ever really existed. But as the humans have their God to worship, so we have ours in the form of the Great Primus.
(NOTE: The bio above is a combination of some of the more relevant information that I found on Primus in my search for any information on him. If anyone has anything that they wish to see differently or be added to this bio please feel free to contact me. I will also take this chance thank Lewis M Brooks from aworldtransformed.com for his assistance in polishing up this bio)