The alien entity in Star Trek: The Motion Picture is V’Ger. It first appears as a vast energy cloud traveling toward Earth, destroying three Klingon ships and the Starfleet monitoring station Epsilon Nine along the way.
V’Ger communicates through an artificial version of Lieutenant Ilia, who is abducted from the Enterprise and replaced by a robotic probe containing her memories. Spock eventually discovers that the enormous vessel inside the cloud is itself a sentient machine, not merely a spacecraft carrying a conventional alien crew.
Near the film’s climax, V’Ger is revealed to be Voyager 6, a 20th-century NASA probe believed lost in a black hole. An alien civilization of living machines found and upgraded it, interpreting its programming as a command to learn everything possible and return that information to its creator.
The entity’s name is often confused with the Borg, the Doomsday Machine, or the Whale Probe. Those are separate Star Trek threats. V’Ger is ultimately seeking its “Creator,” whom the Enterprise crew realizes means humanity.