Creator

Not to be confused with the actual creator of  7th Stand User, known as Clayman.

The Creator is a bonus boss found in the Sanctuary. He is based off the Creator boss of Final Fantasy Legend, and his dialogue is taken and translated directly from the game.

The God-Slaying Axe
After defeating Alessi, talk to him in the Sanctuary, and he may reveal the location of his axe. Check a certain spot in the river to start a boss fight by choosing the middle dialogue option. Winning will give you an item that will make the following battle with the Creator substantially easier.

The Creator
If Jotaro's level is above 40, talking to the Creator will start a battle. Defeating him will cause him to disappear, allowing access to the door behind, which leads to the Debug Room. Note that he will respawn if you leave the room.

(Note: The dialogue in this battle is a reference to the final battle of The Final Fantasy Legend. There is a glitch in that game that allows the Creator to be insta-killed with a Chainsaw, which is why the item from the event above can be used to defeat him, and also why he will bar you from using Joykiller or Carpenters' Chainsaw attack. The Creator's sprite is ripped directly from the game, and despite the striking similarities, he has nothing to do with Speedwagon.)