The One is an extradimensional entity from before time, in whom Order and Chaos exist in perfect harmony. It created Unicron, then cut him in half to make Primus. The Vok claim to be guardians of The One and followers of its will, possibly meaning it exists in Nexus Zero. They also seem to think that either it created the multiverse, or it is the multiverse. Details are fuzzy.
The Vok were the first known source of information about The One, whom they tended to describe in relation to themselves, or vice-versa. [Note: Capitalization of Vok quotes is at editor's discretion; their lines were printed in all caps.]
The enemy in question at the time seemed to be the resurrected Tarantulas, who in fact had captured the power of two Vok and was preparing to wreak havoc upon prehistoric, post-Beast Wars Earth. The Vok sought to protect "the sleepers," by whom they meant the stasis-locked Autobots and Decepticons aboard the Ark. They believed this to be "the will of The One."
Later, they explained themselves again to their creation, Primal Prime:
That time, they seemed to be referring to The One as not the creator, but the creation. Notably, they never referred to Primus by name (nor Unicron, for that matter), though they did fear "the enemy of all creation," to whom Tarantulas was attempting to deliver the Matrix of Leadership. As Tarantulas would later be seen inside Unicron during the Universe war, Unicron is likely that enemy. This raises the question of how Primus fit into their cosmology, and in fact whether he was what they meant by the creator-One. Answers remain unclear.
DK Ultimate Guide
The One existed before time itself, witness to the birth of the universe. The One was curious about this new realm and created a new being, Unicron, to explore it. For some reason, The One then split its creation in two, one half still being Unicron while the other became Primus. In keeping with their creator's nature as a perfect balance of Order and Chaos, the twin "exploratory heralds" became the embodiments of those two principles, but separated.
- The Armada cartoon, which came out between the 3H comics and the Ultimate Guide, provided an interesting parallel in its creation story. Narration in the series premiere declared, "Light years ago, deep in the cosmos, a unique, digital entity came into being. In search of other life forms, it sent explorers out to the furthest reaches of the galaxy. These digital, mechanical beings became known as Transformers." This was expanded upon in the novelization, which said that the Transformers' pre-war goal was to explore the universe, downloading their discoveries into Cybertron so the planet could grow in knowledge. Assuming the "digital entity" was Primus, he seems to be imitating his creator's own method of vicarious exploration.
- The One's method of creating Primus from the substance of Unicron mirrors Primus's creation of the Transformers, whose sparks are fragments of his own being, as stated in "Abduction". This process was explored in slightly more detail in Simon Furman's apocryphal text story "Alignment".
- The One's (and Primus's, and the Liege Maximo's in "Alignment", and to a lesser extent budding) method of splitting off portions of its lifeforce all have a strong correspondence with Emanationism, specifically the Gnostic flavor, wherein an all-powerful God known as "The One" responds to the unresolvable conflicts in the world by "emanating" polarized aspects of itself to fight them out until they achieve resolution and then return to enlighten The One with their findings. (William Blake wrote a tiresome cycle of epic poetry about one such conflict.)