Gary Seven was a Human male whose ancestors were abducted from Earth around 4000 BC. He held the position of Class One Supervisor, known as Supervisor 194. He was grown and conditioned in some way which allowed him to have a completely healthy and flawless body; furthermore he was insensitive to the impact of the Vulcan nerve pinch.
Using advanced alien technology, including the Beta 5 computer hidden in his office in Apartment 12B at 811 East 68th Street in New York City, he continued the dead agents' mission to make sure mankind did not destroy itself with nuclear weapons.
When his transporter beam was intercepted by the USS Enterprise, it appeared that the Enterprise crew would prevent him from stopping the upcoming launch of a nuclear missile. His efforts were eventually successful. Seven used the Beta 5 exceiver circuits to cause the third stage of the American rocket to malfunction. It veered off course and the warhead exploded 104 miles above ground. This caused the nuclear powers to re-assess the risks of an orbiting nuclear platform.
He remained behind on Earth to carry out other missions with his assistants: Roberta Lincoln, a Human female from Earth of that time period to whom he accidentally described his mission, and Isis, his mysterious cat. (TOS: "Assignment: Earth")