J. Allen Hynek
Josef Allen Hynek (1910 - 1986) was an American astronomer, professor, and UFO researcher. He participated in an advisory capacity in three U.S. Air Force UFO studies: Project Sign (1947-1949), Project Grudge (1949-1952), and Project Blue Book (1952 to 1969). After the conclusion of these projects he continued to conduct his own independent UFO research.
In his 1972 book The UFO Experience: A Scientific Inquiry, Hynek suggested a means of identifying UFO encounters which became known as the Close Encounter classification system.
1st Kind: Sighting of one or more UFOs.
2nd Kind: Sighting of a UFO with associated physical effects (e.g. heat, electrical interference, etc).
3rd Kind: Sighting of an animated being (presumably an alien but not specifically defined as such).