Erich von Däniken is the author of Chariots of the Gods
, proposed a theory as to how man came to colonize or inhabit earth. Because it is only a theory, there's no definitive evidence or proof of ancient astronauts. His theory is as good (or as bad) as anyone else's. He's sold millions and mill-l-l-ions of books and has been translated in several languages. More power to him.
The selling of these books he wrote helped him settle some financial problems with back taxes and fines for embezzlement for which he was imprisoned. This issue doesn't reflect on the quality or veracity of his authorship, however.