The Third Man
John Grigsby Geiger is an American-born Canadian author. He is best known for his book "The Third Man Factor: Surviving the Impossible", which popularized the concept of the "Third Man", an incorporeal being that aids people under extreme duress. The book is the basis for National Geographic Channel's "Explorer: The Angel Effect", in which Geiger appears. A book of the same name was published in 2013.