The Voice in the Void

Story, first published: Wonder Stories Quaterly, Spring 1932

The story is standard interplanetary adventure except for the ending. In his curiosity to solve the mysteries of the Martian religion and to wreak vengeance on the Martians for putting his buddy's brain in a cylinder, the hero discovers a terrible secret that ordinary, money-grubbing Earthmen had visited Mars a million years ago and the Martian messiah was really a terrestrial.
Surveying stories of religion in American pulp magazines, Sam Moskowitz calls "Voice in the Void" the first of Simak's "sacrilegious" science-fiction stories, identifying Simak as one of the first to use this "delicate topic."

Ewald, Robert J.: When the Fires Burn High and the Wind is from the North, p.24