The Monster Society of Evil

Obviously, the guy with a banjo and the straw hat is the worst of them all.

The longest serial of the Golden Age of Comics, running from Captain Marvel Adventures #22 to #46. Features one of the earliest examples of a Legion of Doom, though was possibly meant as a metaphor for Nazis.

Tropes used in The Monster Society of Evil include:

• Amoral Attorney: This is subverted in the last chapter of the The Monster Society of Evil as Mister Mind is being tried, his lawyer, who he knows to be a slick Amoral Attorney, hears of Mister Mind's crimes and tells Mister Mind he hopes he gets the electric chair, showing Even Evil Has Standards.
• Big Bad: Played with. Mister Mind, as evil as he is, is only a three-inch worm.
• Bound and Gagged: Happens frequently to Billy Batson, often at the end of serials, preventing him from saying his magic word.
• Cliffhanger Copout: After Captain Marvel spends a large portion of one serial trying to stop a giant shell fired from space striking Russia, this happens.
• Earthshattering Kaboom: Nearly happens a couple of times, Mister Mind tries firing giant shells at America and Russia from a ten-mile Big Bertha, then in another chapter he tries to blow the Earth in half using explosives set up by tiny Americans living underground in case the war went badly for America.
• Hydra Problem: The Monster Society of Evil has a literal Hydra created by Mister Mind, which when it loses a head grows it back with the head of another animal. Captain Marvel causes its heads to fight over meat, killing it.