E Cayce

The man said in a reading, published in a book called "Sugai River".
Their here and here to prevent mankind from anhiliating all inhabitants and leaving this Planet cordoned off from further life for more than hundreds of years.
I believe George Adamski was right.

Decoy

There is nothing to fear but fear itself. No blood thirsty ignorant lifeform is EVER going to be able to handle the technology it requires to travel through space to other solar systems.... hell the nuclear generators we have that power the satalites we use was almost enough to do us in.