The Aliens commonly called "grays" were first encountered in the Roswell incident in 1947. They were secretive, non-communicative, and semi-hostile in many ways. Positive contact was never made.
Reports of grays tapered off in the 70s and there are no reliable reports of grays after 1981.
It is now understood that Team Alpha got most of its advanced technology from the grays, indirectly by stealing the Roswell wreck.
Reliable information on the grays is near totally missing due to the interference of Team Alpha. None of their records have been recovered with the missing artifacts and bodies likewise.