In the primitive age following the departure of the Knights of Cybertron, Micronus Prime came to rule a sector of the planet before he and four other Primes joined eight others in the Crystal City alliance, forming the Thirteen Primes. The Primes ruled their planet until civil war broke out. Like eleven of his siblings, the death of Nexus Prime prompted Micronus to abandon Cybertron. With his Titan Prion, he colonized a distant planet and oversaw a civilization of Mini-Cons. When the Black Block Consortia found the colony however, Micronus fled via Prion's Space bridge leaving his people to die. Though Cybertronian legend would say that Micronus had returned to the Well of All Sparks, Sentinel Prime knew this to be a lie, knowing Micronus had simply fled but did not know where the Prime had absconded.
Micronus had in fact created the sub-atomic realm of Microspace and retreated inside it.
His inert, planet sized (relatively speaking) body lay at the very center of the universe until it was found by Baron Karza, searching for a solution to the entropy cloud. Given that the cloud warped space/time, the Baron was able to spend years studying his creator's body and discovered the Prime's personal Spacebridge which allowed passage back to Micronus's home dimension, where he discovered Ore-13. Though Micronus's body was inert, his spark still burned and he managed to contact his old friend Metrotitan to speak to Optimus Prime about sending Ore-13 samples to Microspace. A miscommunication resulted in Windblade being sent instead though she promised to pass the message along to Optimus. After Windblade had learned about Microspace's problems, Micronus urged her to do whatever it took to to save his realm. However the cityspeaker discovered Optimus did not trust Micronus and tabled the discussion until the current threat had passed to Rom's quiet displeasure. The Micronauts made their way to Micronus's body tracking the energy of his spark as a power source but were greeted by Karza who introduced them to their god. Their prior psychic contact had linked Micronus's and Metrotitan's Spacebridges. When Karza activated the Prime's Spacebridge, the Titan responded and Rom used the link to send several samples of Ore-13 into Microspace, much to the Baron's rage.
After Karza had made an attempt to use Ore-13 to save Microspace only to be forced back by the heroes of Earth, he instead opted to colonize Earth as a new home for the denizens of Microspace. As he drew up battle plans, Karza pondered the possibility of enerchanging with his creator while keeping in mind how the Time Travelers trying to enerchange with time had caused the entropy cloud in the first place. Ultimately, Karza decided the risks were worth the reward and fused with his creator, inheriting some of his memories of the Thirteen Primes and the Prion colony. Wearing Micronus's body, Karza returned to the sight of his banishment and overpowered Optimus Prime in a vengeful rage before he set out to find the Micronauts. Karza mused however that Micronus's persona was overriding Karza's own and the Baron was losing himself to the Prime. Nonetheless, Karza was assured of his victory over Earth, convinced that the Prime's power was superior to all the human super-villains. Karza again enerchanged with Micronus to fight off Optimus before the two were forced to ally themselves against a Time Traveler empowered Shazraella. Using her powers however, Shazraella was able to separate Micronus from her husband and send the ancient Prime hurtling through time.
- Micronus Prime debuted as an unnamed background character in the 2011 Transformers: Prime episode "One Shall Rise, Part 1" before receiving his name in Transformers: The Covenant of Primus. The IDW incarnation was first mentioned in 2015's The Transformers #47 before debuting on-panel the next year in Micronauts: Revolution.
- Micronus Prime at TFWiki