The Devil appeared to tempt Earl Sinclair in the fourth season Dinosaurs episode "Life in the Faust Lane." The Devil makes a deal to trade Earl's immortal soul for a collectible Fernhill mug, Cap'n Willy, the Ol' Salt. The Devil does so, boasting that he's the king of lawyers, and is presently suing the canned ham manufacturers for borrowing his likeness. Earl discovers a warranty on the mug, however, and so is able to stave off the Devil, who reluctantly restores everything the way it was prior to the fateful bargain.
The deal with the Devil is a reference to Faust, a German legend about a scholar who makes a deal with the Devil, selling his soul in exchange for knowledge and worldly goods.