Okay, we're going to follow the winding course of a joke, from its (possible) origin to its (possible) inspiration for "The Funniest Joke In The World", a "killer joke" so lethally funny the listener / reader will literally die laughing. Here are the strips (courtesy Steven Thompson's Four-Color Shadows blogspot) for an eight week Li'l Abner continuity from Dec. 26, 1964 to February 12, 1965, officially credited to Al Capp but (possibly) ghosted by Bob Lubbers.
Several variants of this basic idea exist, but the actual "killer joke" seems to have originated with Lord Dunsany's "Three Infernal Jokes" in 1916. Capp's Li'l Abner used the idea in 1964; did he crib it from Lord Dunsany or was it an idea he originated on his own? Monty Python's version was first shown about 2 1/2 years later on Oct. 5, 1969, but while the Pythons were certainly aware of Li'l Abner did it serve as their inspiration or did they harken back to Lord Dunsany?
coda: Hudson & Landry were a pair of Los Angeles DJs who had a string of novelty / comedy records between 1971 and 1974. In their skit "The Prospectors" (a.k.a. "I Couldn't Live Like That") they appear to have appropriated Capp's capper at the 3:24 mark...
thanx to Tom Spurgeon The Comics Reporter for the tip-off