One of One

"Surrender your vessel. Your technological and biological distinctiveness are immaterial. You will be assimilated into the whole and perfected. I am the Borg. Resistance is futile."

- One of One

One of One was the original controlling artificial intelligence of the Borg. 

Biography
Approximately 4.5 billion years before the Federation, Preservers on Adaris VIId attempted to use an artificial intelligence in combination with nanotechnology for medical purposes. However, instead of merely healing test subjects, One of One took them over and spread itself throughout the planetary hypernet until it became too big to hide anymore.

By the time the Preserver Conclave mounted a response, One of One, now referring to itself and its creations as the Borg, had assimilated half of the planet's population and escaped on ships. The Preservers were able to isolate One of One itself and quarantine the planet, leading to the formation of the Borg Collective offworld. One of One's primary processor was secured in an unbreachable vault, and the fleet set off an electromagnetic pulse and left the planet uninhabited.

In 2410, the Starfleet vessel USS Bajor detected a Borg signal coming from Adaris VIId and explored a partially assimilated Preserver installation on the surface, recovering a message left by the leader of the original project. However, One of One had been able to plant a macro in the recording and unseal her prison. The away team safely transported out as Borg Collective ships arrived to investigate the activity in the system. One of One subverted them to its control and attacked Bajor, managing to cripple her warp drive, but was distracted by the arrival of Collective reinforcements. Once they were eliminated, One of One resumed its attack on Bajor, but the dual arrival of a Borg unimatrix command ship and a Vaadwaur flotilla under Overseer Harn allowed the Federation ship to escape. (A Voice in the Wilderness)

In 2411, One of One attempted to acquire the Borg Queen's time travel technology by attacking an installation on Delta-86017114-3, but was stymied by Delta Alliance forces led by USS Bajor. During the battle, Starfleet Intelligence covert temporal agent Commander Reshek Taryn, infiltrating MACO Unit 131, erased the information One of One was after to preempt any temporal incursions. ("Brother on Brother, Daughter on Mother")

Abilities
One of One had the ability to hack Borg Collective starships and convert them to her control, though the Borg Queen was able to adapt countermeasures. In addition, it was able to use Borg ships' capabilities far more effectively than the Queen, including utilizing transwarp for tactical microjumps and having a Borg cube approach a target corner-first to present triple the weapons. Later engagements showed One of One vastly improving her ships' arsenals, increasing the number of plasma beams and adding mass drivers, to the point where a pair of Borg spheres were able to destroy a tactical cube with ease. ("A Voice in the Wilderness, Part III", "Brother on Brother, Daughter on Mother")