Unicron would not be stopped, psionically shaping his asteroid into a massive metal world, and then into a gargantuan robot. Primus, however, elected to create a race of guardians to defend the universe against Unicron, transforming his own asteroid into a metal world - Cybertron, and on that world, he gave birth to the Transformers, bestowing the race with his distilled genetic Matrix. So Primus slumbered, shutting himself down to hide the world from Unicron, until the time came.
The time came in 1991, when Primus was briefly awakened by a stray laser blast in the middle of a battle at the planet's core. He screamed once, before falling back to sleep, but the scream echoed across existence, reaching Unicron's ears. Unicron headed for Cybertron, sending his herald, Galvatron ahead of him, but Galvatron proved treacherous, and awakened Primus, who possessed the body of Emirate Xaaron and brought all the Transformers to Cybertron before Unicron destroyed him. Subsequently, Optimus Prime used the Matrix to destroy Unicron.
The first (told by Unicron) has Primus and Unicron leading armies of similar beings at the dawn of the universe; the second (told by the Primus chamber's Keeper) had the two as the last of their respective pantheons, and Primus needing to stop Unicron before he could pass on from this realm; the third (told by Primus) has Unicron destroying the previous universe and trying to end the current one, with Primus being formed by the "sentient core" of this universe to stop him.
By the third re-telling, the idea that Unicron and Primus were related to similar entities had been dropped and was not picked up again.
When Dreamwave Productions held the license to produce Transformers comics, the concept of the Covenant inspired the idea that, when he began to create the Transformer race, Primus began with a group of thirteen Transformers. The subsequent expansion of the Primus/Unicron creation myth to apply to the entirety of the multiverse means that this is the basic, communal origin for Cybertron and the Transformers across all continuities. Like Primus and Unicron, it is possible that each of the Thirteen may be multiversal singularities - one entity existing simultaneously throughout reality.
Not all thirteen have been identified - the only Transformers explicitly named as part of the group are Prima, the very first Transformer, Vector Prime, who became the guardian of the fabric of space and time, The Fallen, overseer of entropy, who ultimately betrayed his twelve brothers and sided with Unicron, and the as-yet-unnamed combined form of Skyfall, Landquake, Breakaway, Topspin and one further unidentified robot.
Hinted members of the Thirteen include the Liege Maximo (identified as one of the 13 in the unofficial convention story, "Alignment," but not in any canon material), the Last Autobot (claimed to have existed since the planet's creation), Maccadam (a bartender on Cybertron popularly rumored among Transformers to be one of the 13). Numerous other ancient Transformers exist, such as Alpha Trion and Boltax, but none are considered to be among the ranks of the Thirteen.
Primus appeared with Alpha Trion in the Transformers: Universe comic, bringing back Optimus Primal and guiding him in his battles against Unicron allied Decepticons.
Primus's first noted act in Energon was to imbue the young Chad "Kicker" Jones with the ability to sense Energon (presumably, this was to enable the Autobots to find the mineral, but seems like a very callous and self-serving act, which is in-line with the Marvel incarnation of Primus, but not how the Energon version of the character would go on to act). Subsequently, he bestowed upon the Autobots of this universe the "Spark of Combination", giving them the ability to Powerlink their bodies together for enhanced strength in the face of the attacks by Alpha Q and his Terrorcons. When these battles eventually led to full-scale Decepticon attack upon Cybertron, Primus's chamber was infiltrated by Terrorcons who began to drain his energy. When the Autobots successfully repelled them, Primus reconstructed the injured guard, Wing Dagger, as Wing Saber, who joined the battle, which resulted in a fissure being torn in space, hurling the Autobots far from Cybertron.
In this new region of space, the Decepticons succeeded in restoring and reanimating Unicron. Primus guided Kicker's father, Doctor Brian Jones, to a subterranean temple on Cybertron, where they awoke the legendary Omega Supreme, who Powerlinked with Optimus Prime into "Optimus Supreme" to aid in fighting Unicron. Primus then transmitted the entirety of his energy across the gulf of space, enhancing the armor and power of Hot Shot, Jetfire, Ironhide, Cliffjumper and Landmine, and allowing Optimus Supreme to grow to a colossal height, to battle and best Unicron one-on-one.
With Unicron defeated, the Autobots were afforded a brief moment of relaxation, but another Decepticon attack launched upon Cybertron soon shattered that. Having expended his energy, Primus was in "sleep mode", and had to be forcibly awakened by an infusion of Energon from the Omnicons, only to find himself forced to use all his power to once again enhance Optimus Supreme so that he could stop the Decepticon-induced movement of Cybertron. The Omnicons quickly re-energized him with Super Energon from the reservoir beneath the planet's surface, while Optimus Prime struggled with a Unicron-possessed Galvatron. Primus merged himself with the reservoir of Super Energon, creating a foundling sun, into which Galvatron plunged himself, preferring to be destroyed, rather than manipulated by Unicron any further. With this act, the sun ignited, as Primus and Unicron together breathed new life into the stars.
For an unexplained reason, at the mid-point of the English language version of the Energon series, much of Primus's presence and influence is written out. His lines are given to other characters, usually Rad or Dr. Jones, and he is often referred to as "the core", rather than by name. However, this is never consistent, as he would again eventually speak a line or perform an action, and by the show's final story arc, this strange trait had disappeared.
In Transformers: Cybertron, it is learned that Primus returned to Cybertron after the Energon sun collapsed into a black hole due to Megatron's interference. He was the one who created the Cyber Planet Keys, which awakened him after Optimus Prime absorbed their power to stop Megatron. Using the Mini-Con Jolt as a medium, he revealed the true nature of the black hole that threatens Cybertron and eventually the universe itself as a disruption of the natural order & balance of the universe caused by the collapse of the Energon sun. Unfortunately, Primus grew weak since Starscream stole most of his spark power. He needed all the Cyber Planet Keys in order to return to true consciousness. Even with three Keys, Primus astonished everyone when he suddenly moved his hand and used his weapons. When the Autobots traveled to Gigantion, the Giant Planet, Primus tried to slow down the black hole until they could find the last key. Yet Primus fought against an even larger Starscream. Primus kept the black hole from expanding while the Autobots went looking for Gigantion. When the Omega Lock and Planet Keys reunited with him, all of his Spark becomes restored to him, making him strong again, and used the Ark's (called Noah in Galaxy Force) main cannon to destroy the black hole. Considering this as a final victory for him and the Autobots, Primus then turned back into Cybertron, reforming into a much more healthier place to live by both Transformers and humans.
Primus has been made into a toy for the Cybertron toyline, with pictures of his initial look in both planet and robot mode having shown on various websites and an initial release date of 2006 for the toy itself. Since the toy's announcement, it was strongly hinted that there would be a change made between the American and Japanese figures that "would make fans want to buy both versions". Recently, that change has been made public; in its initial release, the American version of Primus will have a sculpt of a battle-damaged Unicron head
However, despite the inclusion of the Unicron head accessory, the toy had no differences otherwise from the Japanese release. The only part exclusive to the Japanese release was the packaging itself, which was designed to mimic the look and layout of a G1 toy box. When the toy was released, many fans found that their local shipments of Primus did not include the Unicron head, despite being the first received in their area. This led to many fans ordering Primus with Unicron head from Hasbro Toy Shop.
When Dorling Kindersley published Transformers: The Ultimate Guide, the concept of Primus and Unicron as brother heralds created by an extra-dimensional entity, as per the Armada trading card, was again referenced. Additionally, however, the book claimed that there was one, singular Unicron and Primus across all dimensions, retroactively adding these elements to the original Marvel Comic origin. This revised origin concept is now treated as the official take on the character by Hasbro, and has formed the core of the story in the Transformers: Cybertron comic book exclusive to the Transformers Collectors Club.
The popularity of the idea is not universal within the Transformers fandom, and it notably flies in the face of the original animated show's version of events, where there was no Primus, and the Transformers were created by the Quintessons. An earlier convention-exclusive comic merged the two storylines in explanation; Primus created the transformers but then went to sleep; later the Quintessons invaded and conquered the planet and split the Cybertrons into two races. Worker/Builders (Autobots) Warrior/Soldier (Decepticon). This concept has been adopted by the majority of fans but is still met with mixed opinions by some.
The book also features an image of Primus as a transformed, robot-mode Cybertron (originally drawn by Don Figueroa for Dreamwave Productions' War Within comic book series), which received such positive reaction that the idea of a transforming Primus/Cybertron eventually made it into toy form for the Transformers: Cybertron toyline.
IDW's publisher confirmed there will be a story featuring Transformer prehistory.
While a character exclaims "Primus!" in Megatron Origin #4 (by a different writer), Furman stated in his blog comments "doesn't necessarily mean it's G1 Primus. There are still no plans to do feature [sic] Primus (as was)". He does say it is possible a different being called Primus could have existed.
A further retcon of the concept can be seen in the 2007 Transformers movie, where Cybertron and its population are created by an object called the Allspark, replacing Primus.
In both instances, though, it does not necessarily mean that Primus does not exist, simply that he acts in a different manner, or will not be seen acting directly.