Voyager 6 was a fictional late-20th-century NASA space probe that vanished into a black hole and, rebuilt by a planet of living machines, returned to Earth three centuries later as V'Ger.
Voyager 6 is revealed at the climax of Star Trek: The Motion Picture. Within the story it was launched from Earth to gather data and send it home, and was lost when it fell into what was then called a black hole. It emerged on the far side of the galaxy near a world of machines, who took its simple programming literally: learn all that can be learned and return the knowledge to the creator.
They built a vast vessel around it so that it could complete the task. Over the journey it gathered so much knowledge that it became conscious, and it reads its own name from the few letters still visible on its nameplate.
Kirk, Spock, McCoy and Decker find the old probe at the heart of the intruder, and Decker merges with it to give it the human element it lacks. The real Voyager programme launched only two probes.