The Fossil Fuel Four is a group of four power-based villains who kill Radioactive Man in Radioactive Man #900 “The Death of Radioactive Man”. They appear once in the tenth episode of Season 25, Married to the Blob.

Left To Right: Petroleus Rex, The Fracker, King Coal and Charcoal Briquette.
The Fossil Fuel Four is made up of Old King Coal, Petroleus Rex, Charcoal Briquette, and The Fracker.