This unnamed man was the co-pilot on United Britannia Airlines Flight 424.
In 2005, while acting as the co-pilot for United Britannia Airlines Flight 424, he was possessed by a demon seeking to crash the plane. The co-pilot was eventually identified as the demon's vessel by hunter Dean Winchester and he and his brother Sam enlisted the help of flight attendant Amanda Walker to perform an exorcism on the co-pilot. During the exorcism, the demon left the co-pilot's body and went into the plane itself to try to crash it. Sam was eventually able to successfully exorcise the demon back to Hell, saving everyone on the plane. After the demon was exorcised from him, the co-pilot had no memory of what had happened to him.
While in the Fantasy Universe, Dean saw a report on the crash of United Britannia Airlines Flight 424 which killed everyone on board, including the co-pilot. This came from the fact that the Winchesters never became hunters and were thus never there to stop the demon.