V'Ger

V'Ger was a extraordinary machine entity encountered by the Federation in 2273. The entity's surrounding energy cloud was over 2 AUs in diameter and generated huge amounts of power, which worried all in the Federation when it was detected on a direct heading for Earth.

With the entity being over 54 hours from Earth, Starfleet rushed the refit of the USS Enterprise so that it could be launched in time to intercept V'Ger. After penetrating the huge entity and traveling to the center, Admiral James T. Kirk and his crew encountered V'Ger, who absorbed Enterprise helmswoma Ilia, and ttthen discovered that V'Ger was actually the NASA probe, Voyager 6'', that was launched from Earth in 1999 and had entered a black hole, that had achieved sentience.

V'Ger took its mission to chart and learn everything it could to extremes, as it absorbed everything it was exposed too, and having learned everything, wanted to return to Earth to part its knowledge and join with its creator. Realising that the fate of Earth was in their hands, Commander Willard Decker joined with the entity and programmed the information it needed to transmit its data. Once the two were joined, the entity evolved onto another plane of existence and headed for the Andromeda Galaxy. (TOS movie: The Motion Picture and short story: "To Wherever").

Legacy
After encountering the Borg, it was believed that the planet V'Ger landed on was the Central Node and that V'Ger was simply another branch of the Borg Collective that assimilated through the use of energy. (TOS novel: The Return)

However, the Vulcan scientist T'Uerell, after deciphering the secrets of the Borg Collective, uncovered evidence that it was V'Ger who first created the Collective to serve as its heralds in its search for its creator. However, the Borg became strayed from their purpose as the Borg Queen's assumed more power. (video game: Legacy)

Aftermath
The evolution of V'Ger had some wide ranging affects on the rest of the Federation and beyond. On Daran IV, Dovraku and his "Faithful" viewed this as a Sign that the time had come to reinstate the Oracle of the People's control over the Fabrini. (TOS novel: Ex Machina). On planet Mestiko, the defeat of this threat to Earth was used as proof that the Federation could have defended their world from the destructive effects of "the Pulse," and opted not to in order to subjugate the Payav race. (TOS eBook: Mere Anarchy: The Darkness Drops Again)