Greys

Greys are alien species. They are known on Earth as UFO.

History
Greys was always in war with Bohandi. Bohandi was able infected them with specific virus and let them day. To cure that virus, Greys started to visit Earth in the past and abduct humans. They ships and themselves was known as UFO to humans. But after they encountered also time-traveled Jonh Walker's team, they helped them restore timeline. In the meantime, they found cure for the virus. (Aliens)