The Vree are a race of hairless, large-eyed humanoid which had developped a spacefaring civilisation as of the twentieth century. They made contact with humanity in that time, visiting Earth fairly regularly in the 1940s. Not making formal formal contact, they mostly observed and even kidnapped specimens for for further sicentific studies. Vree look much like what human popculture Grey aliens, their behavior also match the character as does their spaceships, shaped like flying saucers. They joined the league of non-aligned worlds in the mid-twenty-third century and later the Interstellar Alliance.
Source: Babylon 5 universe