Robert Collier (1885-1950) was an American author of self-help and metaphysical books. His books have been popular with self-help and New Thought groups. His most known book - The Secret of the Ages - sold over 300,000 copies during his life. In the book "The Secret" Rhonda Byrne writes about it: "The glimpse came in a hundred-year-old book, given to me by my daughter Hayley.