How the heck did they come up with some of the crazy monsters in Dungeons & Dragons? There are a lot of weird, memorable monsters that GMs can use to strike fear into the heart of players — and the inspiration behind them is way different than what you probably expect.
In the 1970s, Gary Gygax found a pack of cheap, plastic "Prehistoric Animals" that had been manufactured in Hong Kong. Some of the toys looked like dinosaurs, and some of them looked like nothing at all. So Gygax based some of monsters featured in the Monster Manual on these strange little creatures.
Tim Kask, a D&D play tester and editor of Dragon Magazine, described the early days of monster invention in a 2007 article:
There once was an unknown company in Hong Kong that made a bag of weird animal-things that were then sold in what once were called dime stores or variety stores for like $.99. I know of four other very early monsters based on them.
Gary and I talked about how hard it was to find monster figures, and how one day he came upon this bag of weird beasts… He nearly ran home, eager as a kid to get home and open his baseball cards. Then he proceeded to invent the carrion crawler, umber hulk, rust monster and purple worm, all based on those silly plastic figures.
The one that I chose was known in the Greyhawk campaign as "the bullet" (for it's shape) but had only amorphous stats and abilities, not being developed. Gary told me to take it home, study it, and decide what it was and what it could do.
Among the monsters that Gygax and friends created in that manner are the Rust Monster, the Owlbear (pictured below), and the Bulette.
You can read more about these "Prehistoric Animals," and see tons of pictures comparing the toys to the Monster Manual, over at Tony DiTerlizzi's blog.