Gary Seven was the major character in the last episode of the second season of the original Star Trek television series.

This episode, entitled Assignment: Earth, was a television pilot for a proposed series about Seven (Robert Lansing), who was apparently a humanoid from the distant future (well beyond the 23rd century time frame of the original Star Trek) or someone sent by space aliens to prevent the Earth from destruction by its human inhabitants or to prevent them from contaminating a large portion of the universe with radiation. Seven is encountered by the crew of the Starship Enterprise, who have been sent back in time by orders of the United Federation of Planets to find out what actually had occurred on Earth in the late 1960s, which was the "present" at the time of the production of the original Star Trek series. Seven's secretary, "Miss Lincoln", was portrayed by Teri Garr. They all work together to prevent a nuclear weapon from achieving low Earth orbit, which apparently was to be the precursor of a devastating worldwide nuclear war.

Some Star Trek purists resent this episode, as time travel, never before presented as a capability of the Enterprise or 23rd century technology in general, was suddenly represented as seemingly almost routine, and also for the conclusion, in which it is determined that the time travel of the crew was just "part of what had happened on that day in 1969".