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Transformers: Generation 1
Near the beginning of the universe, the being known as Primacron existed. Possessed of tremendous intelligence and an indefinite lifespan, but diminutive physical form, Primacron chose to be a creator, developing primitive mechanoids, one of which became his assistant as he continued his work. His creations continually grew greater, larger and smarter, until finally, he created the world-eater, Unicron. The megalomaniacal Primacron planned to use Unicron as an instrument of his will, sending him to consume world after world, to wipe out all life in the universe, leaving it a blank slate for Primacron to do with as he wished. But Primacron's creation was too intelligent - Unicron decided that he would be his own master, and turned on Primacron, gravely injuring the tiny being before voyaging out into the universe to fulfill his destiny.
Eons passed, and Primacron recovered from his wounds, turning his attention to creation once again, still seeking to fulfill his original goal. In the Earth year 2006, Primacron unleashed his new creation, Tornedron, on an unsuspecting galaxy, and Earth, Cybertron, and most of the Transformer race fell victim to his energy-draining abilities with sudden, terrifying ease. However, one last hope existed in the form of a group of Transformers gathered together by Primacron's old assistant. His body destroyed in Unicron's attack, the assistant's essence had fled to a dead world at the centre of the galaxy. Realizing the madness of Primacron's ambition, the assistant - called "Oracle" in the episode's script, though not given any name in the episode itself - summoned a group of animal-themed Transformers to his world, hoping that their primitive instincts would prove an effective counter-force to Primacron's intelligence. Alas, moving under Primacron's direct control, Tornedron defeated and drained all of them, save for Grimlock, who was left for dead when Trypticon collapsed on him. Grimlock survived the ordeal, however, and proceeded to track Tornedron back to Primacron's world, where he confronted the scientist and was particularly amused by his stature. Tornedron, however, interrupted Grimlock's merriment by making it apparent that he too had attained independent thought, and as he bore down on Primacron's world, intending to consume it, Primacron attempted to calculate the proper course of action to defeat his creation. When the complex plans failed, the simple-minded Grimlock randomly flipped a switch on the control panel, reversing Tornedron's energy polarity and dissipating him. Although Primacron was suitably impressed by Grimlock's direct actions, his relief soon turned to dismay when Grimlock's joyful victory celebrations decimated his laboratory.
The preceding events can be found in the 3rd season of The Transformers in the episode entitled "Call of the Primitives."
Primacron appeared in the TFcon 2008 voice play "Primitive Recall," in which his planet is once again visited by several of the "Primitives" as well as other Autobots and Decepticons in response to the threat of a "repeat repeat wave." However, this later proves to be a ruse by Grimlock, who with his fellow Transformers-including Nightbird-proceeds to demolish Primacron's lab yet again before taking him prisoner, something he regretted not doing previously given the threats Primacron had unleashed on the universe. 
Ask Vector Prime
Primacron is also featured in several "Ask Vector Prime" stories, typically posing a threat to reality through his machinations. In one such story, the actions of the Decepticon tyrant Megazarak in one reality decimated the Transformer race, leaving no one to stop Tornedron from destroying that universe, Primacron included. In another, Primacron learned of alternate realities where the Transformers had been created by Primus during the course of a trial for his various crimes, and came to the conclusion that such universes were abominations. He thus developed a powerful device to destroy the very fabric of reality, prompting the Protectors of the Transformers: Alternity universe to stand against him. Using his powerful armor Solduron, the Macro-Avatar, he defeated his foes and destroyed them with the exception of a version of Optimus Primal, who survived due to previous existence as a being without physical substance. Primal soon convinced Primacron of the error of his ways, and the ancient scientist departed for parts unknown.