V'Ger is the main antagonist in Star Trek: The Motion Picture. It is an alien force, hidden in a massive cloud of energy, moving through space towards Earth.
The cloud destroys three of the Klingons' new K't'inga-class warships and the monitoring station en route. Later on in the movie, The Enterprise intercepts the energy cloud and is attacked by an alien vessel within. A probe appears on the bridge, attacks Spock and abducts the navigator, Ilia. She is replaced by a robotic doppelgänger, a probe sent by "V'Ger" to study the crew. V'Ger itself, is a living machine.
At the heart of the massive ship, V'Ger is revealed to be Voyager 6, a 20th-century Earth space probe believed lost. The damaged probe was found by an alien race of living machines that interpreted its programming as instructions to learn all that can be learned, and return that information to its creator. The machines upgraded the probe to fulfill its mission, and on its journey the probe gathered so much knowledge that it achieved consciousness.
Spock realizes that V'Ger lacks the ability to give itself a focus other than its original mission; having learned what it could on its journey home, it finds its existence empty and without purpose. Before transmitting all its information, V'Ger insists that the Creator come in person to finish the sequence. Realizing that the machine wants to merge with its creator, Decker offers himself to V'Ger; he merges with the Ilia probe and V'Ger, creating a new form of life that disappears into another dimension.