A Dragon in the Metroid series is a seahorse resembling creature that first appeared in Metroid for the NES. It possesses the ability to spew fire balls out of its snout. They live on Norfair in Zebes, though it's clear that all of the Dragon inhabitants of Zebes were killed off once the planet was utterly destroyed. It's possible that other members of the species lived elsewhere, though it's currently unknown.
Despite the fact that they look like a seahorse, they live in molten-lava filled areas, where they rest inside of the lava, waiting for an opponent such as Samus Aran to appear. Their armor that covers their body is so powerful, probably thanks to the lava it lives in.