Fredric Brown 
Mind Thing [EPUB ebook] 

"HE" was really an "IT"He was incapable of love or mercy, or hate. And he certainly never felt the lack. He was almost pure thought.He was just doing what he had to do — looking for the right body to play host to him. Once he found it and moved in, he would execute one of the most incredible plans ever conceived. He would be hailed as a hero on his own planet and…EARTH WOULD NEVER KNOW WHAT HIT IT!