The Fearsome Five first appeared in The New Teen Titans #3 - The Fearsome Five.
The original roster is as follows:
The Fearsome Five was a group put together by Doctor Light when he placed an ad in the Underworld Star, a criminal underground paper.
Doctor Light was the self proclaimed leader of the group; however, Psimon used his telepathic powers in order to take control of the Fearsome Five and use them in his plans to destroy the world. This angered his team mates; however, and they made a pact to team up on Psimon when the time was right.
Psimon was eventually assumed dead after an encounter with Trigon; however, it turned out that he had only been banished to another dimension. Psimon sought help and sent a telepathic message to the other members of the Fearsome Five asking for help. The other members initially didn't want to help him considering how he used his mental powers against them, but they agreed to let him in, secretly planning to kill him should he get out of hand.
The group eventually helped Psimon; however, in their battle against the Teen Titans they were defeated.
The Fearsome Five later encountered Superman, with a new lineup: Mammoth, Gizmo, Shimmer, Charger, and Deuce.
The team disbanded once again shortly after that. Sometime later, Psimon returned from certain death and systematically sought revenge on his former teammates: Gizmo, Mammoth and Shimmer. Mammoth barely survived although his sister Shimmer seemingly perished. Gizmo later resurfaced alive. Dr. Sivana gathered the team - Psimon, Mammoth Gizmo and Jinx - and was able to successfully restore Shimmer to life. The revamped Fearsome Five is a deadly team, if they can keep from killing each other!