Professor Jeff Carlson was a Human scientist in 1947, when the three Ferengi, Quark, Rom, and Nog, crash-landed in Roswell, New Mexico, after having accidentally traveled back in time from the year 2372.
Along with his fiancee, Faith Garland, a nurse with the US Army Air Corps, he was assigned to the team investigating the three aliens, whom the military feared were part of an alien invasion force. In that capacity, Carlson initiated the attempts to communicate with the Ferengi, a task which was impossible until Rom was able to repair their universal translators. Later, when General Rex Denning ordered the Ferengi interrogated, Carlson and Garland were assigned to assist Captain Wainwright in his attempts to extract information from them. When it became clear, however, that Wainwright was willing to exact physical harm to the Ferengi, they incapacitated him and helped the Ferengi escape. They subsequently took them to Hangar 18, where their ship was being stored, allowing them to leave and return to their own time by recreating the time warp which transported them back in time in the first place. (DS9: "Little Green Men")
According to the novel The Rise and Fall of Khan Noonien Singh, Volume 1, he and Faith were married as planned after the events of "Little Green Men". He was subsequently employed at Area 51. In 1986, Project F (as Carlson's operation was known) had a burst of activity after Naval Intelligence gave them several devices, namely a 23rd century Klingon disruptor and communicator, recovered from an intruder named Pavel Chekov who had been captured aboard the aircraft carrier USS Enterprise while it was docked at Alameda Naval Base. However, before more than a cursory inspection could be carried out, the disruptor and communicator were recovered by Roberta Lincoln. In the subsequent novel The Rise and Fall of Khan Noonien Singh, Volume 2, it is mentioned that Faith had died prior to 1996, making him a widower.