If we're keeping track of Twain in popular culture, let's not forget the
Riverworld series of novels by Philip Jose Farmer in which a resurrected
Sam Clemens builds a fabulous riverboat and pursues and is pursued by his
archenemy King John (the English one)  along a zillion-mile river in a
galaxy far away accompanied by the resurrected Sir Richard Burton (the
Victorian one), Hermann Goring, and a cast of every human being ever born
(and resurrected).