An evil djinn (demon) and member of the Brothers Djinn.
Calythos is a demon from Earth's distant past. He descibes hmself as a "child of fire" and his body has a theme of lava, both hot and cold, being black with glowing red cracks. His head is like the skull of a dinosaur with the jaw almost detached. He intends to return the Earth to its "pre-human glory" by flooding it with magma after which he and the other Brothers Djinn will rule over it. To acheive this, he carries a flaming sword (he calls it a scimitar and is stored in a scabbard on his back) which only has to be placed in the ground and levered side-to-side to release the lava. In addition, he can absorb a victim into himself and make use of their powers, and when he does this to Parasite he is able to steal the powers of his superhero opponents - and unfortunately their weaknesses.
The volcano that Calythos makes to rise from the sea becomes the site for the Justice League's new base: the Watchtower.