The Old Testament (Genesis 6) and the Ethiopian Book of Enoch (which can be found online) speak of beings who watch the Earth (and have done so throughout time).
Several scientists, Garry Nolan for one (who is a non-believer BTW), have described these beings as having watched humanity for possibly a very long time. In fact, Nolan has referred to them as Watchers, and, as a non-believer, I don't think he knows the Biblical import and meaning of that term.
The Book of Enoch refers to these beings as the Fallen Ones and by other terms.
I am a believer, but am keeping an open mind as to what is going on here.
One fascinating UFO/alien story is the Nevada tall whites described by Charles James Hall.
He was a weather technician for the military who claims he interacted with alien creatures while servicing remote weather tracking “shacks” for the military.
The children of the tall whites look a lot like the standard greys, according to Hall, but the adults are very tall (seven or eight feet).
The children were friendly and played with Hall while the adults were very stand-offish and the males were borderline hostile.
Supposedly the tall whites lived in the Nevada desert for many centuries and had minimal human contact for most of that period.
Fascinating stuff—he is the only documented witness and of course the military is not verifying anything.
If you follow the UFO literature closely there is another tidbit there.
The children were allowed to “play” in small flying craft which are similar to the “eggs” that were seen in three different 1940s New Mexico incidents (Roswell, Zamora, “Trinity”—described in new Jacques Vallee book).
In all three cases small greys were identified by witnesses.
The amusing (or sad) part of all this is that these captured aliens were probably children which undoubtedly added to the confusion of both the aliens and the US military.