Click HERE to see this thread with all of the graphics, features, and links.

the title says it all was it actually like the devil or sea devil or what?

Well we don't actually know. It's never been explained in the story iirc. However, we do know that Vegapunk knows more about the Devil Fruits than anyone. So when he gets involved in the story, he'll probably have a lot of DF exposition to give. Considering One Piece's success, it won't need to be explained so soon though. Perhaps since Caesar is in the story and he knew Vegapunk we might get some info about them but that's a slim chance imo.

Long story short: We dunno. Or at least, I dunno.

They could naturally occur.

They do apparently. But it's weird. Two Devil Fruits of the same type can't exist at the same time, meaning that there aren't two Gomu Gomu fruits in the world and Luffy at the only one. However, after someone dies the fruit can appear again, meaning when Luffy dies the Gomu Gomu will probably surface somewhere.

Here's a hypothesis- they were originally created during the missing era of history as weapons.