Satan Egos is the mysterious high leader of Secret Society Egos and the main antagonist of Battle Fever J.
He is voiced and performed by Shōzō Iizuka.
Throughout history, Egos has manipulated disasters and wars to spread chaos throughout the world. Eventually, his machinations were uncovered by General Kurama Tetsuzen, who forms Battle Fever J to combat the evil overlord.
After the defeat and death of Commander Hedder, Egos formulates a final scheme to destroy Battle Fever J. He has Salome give them instructions to Egos' secret base in order to lure them into a trap. Once Battle Fever arrives at the base, Egos traps them within the Monster-Making Capsule and attempts to convert all of them into an Egos Monster.
However, Battle Fever J manages to escape and destroy the Monster-Making Capsule. Angered by Battle Fever J's continued defiance, Egos enlarges himself to a massive size in order to unleash a natural disaster to destroy all of Japan. Battle Fever form Battle Fever Robo in order to fight him, but are initially overwhelmed and pushed back by Egos' vast supernatural powers. Not able to get close to Egos, the Battle Fever throw their Denkouken at Egos, with the strike killing him instantly and stopping him before he could destroy Japan. With Egos vanquished, all of the Egos beings around the world were also destroyed.
In the end, the true identity of Satan Egos is not explained and therefore forever remains a mystery.