A boy named Bartholomew Cubbins runs into trouble one day when the king rides through town and he finds himself unable to take off his hat, or rather, unable to keep a new one from appearing under it.
This book includes examples of the following tropes:
- Aerith and Bob: There is Bartholomew Cubbins, King Derwin, Sir Snipps, Sir Alaric and the Grand Duke Wilfred.
- Disproportionate Retribution: Bartholomew is interrogated, punished, and threatened to be executed all because he wears too many hats.
- Inverted with Grand Duke Wilfred, who gets a spanking on his behind for all his terrible behavior.
- Early Installment Weirdness: Unlike most Dr. Seuss books, this one is written in prose rather than rhyme.
- Enfant Terrible: Grand Duke Wilfred is the same age as Bartholomew and keeps suggesting to the King (his Uncle) to have him decapitated and pushed off the highest turret.
- Evil Nephew: Wilfred to the King.
- Failed Execution, No Sentence: The main character is sentenced to death for not being able to take his hat off in the King Derwin's presence (a new hat appears on his head every time he takes his old one off). But because the executioner refuses to kill anyone that's still wearing a hat, he has to let Bartholomew go. Of course, given that the executioner didn't want to execute Bartholomew in the first place, it was a convenient excuse not to do so.
- The Hilarity of Hats: The book is about a boy who tries to take off his hat 500 times, but finds that there is always another hat underneath. The hats eventually start getting larger and fancier up until the eponymous 500th hat, which became so fanciful that the king had to have it for his very own...which, thankfully, ended the hat problem as there were no more hats after that.
- Matryoshka Object: Inverted; Cubbins' hat contains an identical hat. Removing the second hat reveals a third hat, which also looks exactly the same. At hat 451, the hats actually start to get bigger.
- Off with His Head!: The Grand Duke Wilfred suggests having Bartholomew's head cut off as punishment for him not taking off his hat in the presence of royalty.
- Punch-Clock Villain: The royal executioner seems pretty nice aside from his job. He objects to executing Bartholomew, who doesn't look worthy of it, and shakes hands with him when it turns out he can't execute him because of the hat problem. (Apparently he's forbidden to cut off a head while it's hatted.)
- Unluckily Lucky: Bartholomew can't take off his hat, which gets him in trouble with the king. (Bad luck.) He can't be executed because he can't take off his hat. (Good luck.) He keeps getting into further trouble because he still cannot take off his hat. (Bad luck.) The final hat turns out to be so impressive that the king pays him a large amount for it and forgoes punishing him for being unable to take off his hat before. (Good luck.)
- The Un-Reveal: It's never explained how hats kept appearing on Bartholomew's head, and even the people in the story don't understand at all how it happened.
- Would Hurt a Child: Downplayed in that the King turns to Bartholomew's execution as a last resort. However, it's worth mentioning that it was because Bartholomew's hat wouldn't come off!