Captain Napalm is a comic book superhero (and an eponymous superhero comic book) in Calvin and Hobbes.
The Captain Napalm comic book is a satire of somewhat outdated superhero comic books such as Captain America. Calvin is a loyal fan of the monthly publication, and even collects Captain Napalm bubblegum cards: for 20$ worth of gum, he got all but #8 and #34. The Captain's comic book is presumably tied in to a "Thermonuclear League of Liberty" comic, as Captain Napalm is head of the aforementioned League. Captain Napalm is never directly featured, and little is known about him.