The Preacher is a character in Sparks Nevada, Marshal on Mars. He has been played by Dave (Gruber) Allen in The Agony of the Feet and Inside Out in Outer Space... Again! and John DiMaggio in Blast from the Past.
In The Agony of the Feet, the Preacher forces both Sparks Nevada and Croach the Tracker to show him their feet to prove they aren't Martians, even though Croach is clearly a Martian. Croach eventually reluctantly agrees to show the Preacher his feet, which forces Sparks Nevada to stimulate Croach's egg sacs until his feet appear. The Preacher is happy with this, and lets them go.
In Blast from the Past, the preacher makes Sparks, Croach, and The Red Plains Rider cocoa while they discuss the upcoming destruction of Mars, and Red's possible romantic decision between Sparks and Croach. The latter is discussed at fiddle-gunpoint, as the Preacher is very interested in the answer.
In Inside Out in Outer Space... Again!, the Preacher keeps Sparks Nevada company while forcing Professor Genius to keep Sparks Nevada alive, as he has been turned inside out and is slowly dying. The Preacher also has a theological debate with Professor Genius about the existence of God.