Medusa was an individual. One of the gorgons. The most famous really because good luck naming the other two off the top of your head. So it made sense that the Medusa became medusas for fantasy gaming. I’m not sure how the gorgon became an iron bull though. That’s just messed up.

The gorgon was even one of the first monsters to appear in the game, being described waaaay back in OD&D in the mid-70s. Maybe it was based on a mini. That apparently happened a lot.

But now it’s in the game. It’s part of the history. So every single new player gets to experience the classic moment of flipping through the monster book and going “what they heck is that?!”