Many sources mention the presence of a being, called J-Rod, at Area 51. There are two main theories with regard to who J-Rod is. Most sources claim J-Rod is an extra-terrestrial, a Grey to be more precise, and most likely from Zeta Reticulum (though it isn't clear whether he'd be a tall grey or not). He would have been part of an exchange programme (See Crystal Knight and Serpo), and his main task here would have been here to provide our scientist with knowledge.
And then there is the version of Dan Burisch. He claims to have been one of the scientists that interacted with J-Rod, and that J-Rod is actually a visitor from the future. In this version, several Grey species would be descendants from mankind, and they would now be visiting us from the future to correct some mistakes that ultimately will have a negative impact on the possibility of the future grey humans to survive. Those mistakes that they want to remedy would lead to acataclysm in 2012, which is what they are trying to avoid. (See also: Tau 9 treaty).