Jackson Roykirk was an early-21st century Earth scientist who created the Nomad space probe – an artificially-intelligent machine sent out with the mission to seek out new life in 2002. Roykirk's ambition was to build a perfect thinking machine capable of independent logic. Spock described him as one of the most brilliant but erratic scientists of his time. (TOS: "The Changeling")
Background information Edit
The photographic image of Roykirk seen in "The Changeling" was "portrayed" by director Marc Daniels. Although he was a 21st century scientist, he wore a standard 2260s Starfleet dress uniform in the photo (albeit it seems to be either a reversed image or configured slightly differently based on the opposite positioning of the "decorations").
In an homage to Star Trek, a character named "Jackson Roykirk" appeared in an episode of Team Knight Rider entitled "Apocalypse Maybe," played by William Christopher of M*A*S*H fame. While this may seem to be a crossover, constant references to "Star Trek" on the show make it unlikely. 
Jackson Roykirk is mentioned in The Rise and Fall of Khan Noonien Singh, Volume 2 as being part of the team which designed and created the DY-100 class ship which carried Khan and his remaining followers to the stars.