Colonel Shaun Geoffrey Christopher was the son of US Air Force Captain John Christopher. He was born some time after 1969 and would become the commander of the first manned mission to Saturn. He was accompanied on this mission by the astronauts Fontana and O'Herlihy.
In 1969, the USS Enterprise, which had accidentally traveled back in time from the year 2267, took aboard Shaun's father Captain John Christopher when he attempted to intercept the Enterprise with his F-104 Starfighter. Initially believing that returning Christopher to Earth would be impossible due to the fact that he might inadvertently change history with his new-found knowledge of the future, Lieutenant Commander Spock eventually realized that he had to be returned, or Shaun Geoffrey Christopher would never be born and the Saturn mission would never take place. (TOS: "Tomorrow is Yesterday"; ENT: "First Flight")
According to Star Trek Encyclopedia, Shaun Geoffrey Christopher was named after writer John D.F. Black's three sons: Shaun, Geoffrey, and Christopher. According to Star Trek Chronology, the mission to Saturn took place in 2009. According to the Star Trek Spaceflight Chronology, the mission took place in 2020.
In the short story "Assignment: One" of Strange New Worlds 8, Gary Seven is assigned to prevent Christopher from boarding one of the airplanes that was involved in the September 11th terrorist attack. Shaun also plays a minor part in Greg Cox's Eugenics Wars novels, where he was meant to be the pilot of the first DY-100 class sleeper ship initially scheduled to go to Saturn. The novel The Rings of Time details the Saturn mission that Christopher commanded in 2020. During the mission, he and Captain Kirk switch bodies due to the effects of an alien probe. Christopher also appears in the Star Trek: Myriad Universes story "Seeds Of Dissent" in Infinity's Prism as the captain of the SS Botany Bay.
Commander Shaun Christopher is the main character of the Star Trek: Live stage show produced by Mad Science Productions and performed at various locations from 2010–2011, including Kennedy Space Center Visitor Complex. The novelization of the episode "Relics" gives the name of the shuttle "loaned" to Montgomery Scott as the Christopher, named for Shaun Geoffrey Christopher, however in the episode, the name Goddard is legible on the hull.