Before the dawn of time, Order and Chaos existed within an extra-dimensional entity known as The One. To explore the fledgling universe, he created the astral being known as Unicron, and then subdivided him, creating his twin, Primus. Both brothers were multiversal singularities, unique in all realities, but whereas Unicron could only exist in one universe at a time, moving between them at will, Primus existed simultaneously in all realities at once. It is suggested, in fact, that the two brothers embody the basic concepts of reality—good and evil, order and chaos—and that their continued existence is necessary for the stability of the multiverse.

As Unicron and Primus went about their appointed task, venturing through the cosmos, it became apparent to Primus that Unicron was a corrupt being, and he took it upon himself to stop the threat posed to all of existence by his sibling. In combat, Primus was no match for Unicron. In cunning, however, he proved himself to be his brother's superior when he shifted their battle to the astral plane, and then back to the physical world once more, only to have both their essences manifest within metallic planetoids, leaving them both trapped. It was with this act of sacrifice that Primus hoped to contain Unicron's evil forever. Unfortunately for him, over time, Unicron learned to psionically shape his prison into a giant metallic planet, and Primus followed suit, becoming the mechanical world of Cybertron. When Unicron then learned to transform his planetary form even further, into a gigantic robot form, Primus adapted the idea to suit his own ends, creating a group of thirteen robots that possessed the ability to change shape, like Unicron.

The war between Unicron and Primus came to its seeming end during a climactic battle in which one of the Thirteen, Megatronus Prime, who would forever afterwards be known as The Fallen, betrayed Primus and became an acolyte of Unicron. The battle ended when the Fallen and Unicron were sucked into a black hole and disappeared from reality. With Unicron gone for now, Primus entered an eons-long slumber, his self-imposed sleep preventing Unicron from detecting him through the mental link the brothers shared.