John Christopher Captain John Christopher was a male Human military officer in the 20th century . He served in the Air Defense Command , a command in the United States Air Force . He had qualified as an expert pilot in this command . His serial ( service ) number was 4857932 . As of 1969 , he was a husband and the father of two daughters . After 1969 , he was the father of Shaun Geoffrey Christopher , the commander of the first successful mission to Saturn . At some point in his career , he was in line for the space program but failed to qualify . In 1968 , he served at the Air Force base of the US 498th Airbase Group . In 1969 , the arrived in low Earth orbit from the year 2267 , through an accidental time warp . Captain Christopher was scrambled in his F - 104 Starfighter to intercept the " Enterprise , " which the Air Force had detected as a UFO . Detecting the approach of Christopher ' s jet , and fearing the use of nuclear warhead s against them , Captain Kirk ordered the jet held in a tractor beam . But the metal of which the jet was constructed proved to be too fragile to withstand the force of the tractor beam , and it began to break apart , forcing Kirk to order Christopher beamed aboard . Christopher ' s arrival aboard the " Enterprise " presented the crew with an interesting problem : Christopher could not be returned to Earth , as his newly acquired knowledge of the future might lead him to alter history inadvertently . With no choice , Kirk informed Christopher that they could not return him , although Christopher refused to accept this . Christopher tried to escape , pointing a phaser at transporter chief Kyle , demanding to be beamed to the surface , but Kirk arrived in time and knocked him out . While Christopher was recuperating in the sickbay , Spock informed Kirk and Christopher that he had uncovered historical evidence that indicated Christopher had to be returned to Earth ; that although Christopher himself had made no relevant contribution to history , his future son , Shaun Geoffrey Christopher , would lead the first Earth - Saturn probe in the early 21st century , and that without Christopher on Earth to father this son , the mission would never take place . Later , Kirk and Lieutenant Sulu beamed down to the Air Force base to covertly retrieve evidence of the " Enterprise ' s " presence in 1969 , but Kirk was captured in the process . Christopher offered to help Spock retrieve Kirk , but only on the condition that Christopher be allowed to accompany the rescue party . Spock agreed , and the rescue of Kirk was successful , but during their time on the base Christopher stole a firearm , with the intention of staying and reporting what he knew . Before Christopher was able to do so , however , Spock incapacitated him with a Vulcan nerve pinch . Spock and Chief Engineer Montgomery Scott devised a plan to return Christopher without any damage to the timeline : they would recreate the time warp via a slingshot effect around the Sun , returning them to their own time . Since , as they gathered speed approaching the Sun , they would initially travel back in time , they would simply return Christopher to a point in time before his transport aboard the " Enterprise . " Their plan worked , and Christopher was returned to the cockpit of his jet before he was beamed aboard , leaving him with no memory of what had transpired - - thereby causing the events he had experienced to " unhappen . " ( ) Appendices . Background information . Captain Christopher was played by actor Roger Perry . According to the episode ' s end - credits , he was credited as " " Major " Christopher . " Of note is that when Christopher was given a Starfleet uniform to wear , its command division tunic bore single full braided metallic - gold stripes ringing its sleeves , indicating the rank of lieutenant . The USAF rank of " captain " is , in fact , equivalent to the US Naval rank of " lieutenant . " Both are O - 3 officer grades in the United States armed forces . The Air Force service number Captain Christopher provided ( 4 857 932 ) was part of an unused range of service numbers ( four million through seven million ) created by the Air Force after World War II but never distributed to service members . The range of Air Force officer numbers in use during 1969 would have had Captain Christopher either holding a three million reserve officer number or , if Regular Air Force , a number somewhere between sixty and eighty thousand . ( " Source : National Personnel Records Center " )