In the season two finale of Star Trek: The Original Series, entitled "Assignment: Earth," the Enterprise travels back in time to 1968. When they arrive in the 20th century, a mysterious man beams aboard the ship. He introduces himself as Gary Seven, portrayed by actor Robert Lansing, and claims to be from the 20th century. Of course, the crew of the Enterprise doesn't believe him, since he just used transporter technology which definitely didn't exist in the 20th century to get onto their ship. After some questioning, Seven reveals that he is actually from another planet and was sent to save Earth, marking one of the first times Star Trek explored this classic sc-fi trope.