Leon Shappe was ruthless killer even before he got his super-powers as Speedfreak. At some point in his life, Speedfreek became addicted to the drug called "snap". He killed the owner and presumable inventor of his battlesuit in order to steal it. Once Speedfreek's daughter, Kate, discovered what her father was doing for a living, she ran away from home. Later, he was hired by a man called only Mr. Lang and had to kill his rival Ralph Badone. Speedfreek succeeded in that job, additionally killing the man's guards. Lang later also hired Speedfreek to kill the man who had infected his son, Tyler, with AIDS. Speedfreek did as told and located Tyler and his partner at a musical performance during an AIDS benefit party. During the battle he injured both Rick Jones and Jim Wilson. Bruce Banner, aka the Hulk was also present. The Hulk ended the battling by literally throwing Speedfreek a very long distance.
Speedfreek image is used in one of the illusions created by Mentallo.
Speedfreek later visited the home of Bruce Banner in civilian attire. Bruce doesn't yet realize that this is actually one of his old foes. Speedfreeks want the Hulk to find Larry Richards, the one responsible for murdering his little girl. The Hulk goes to Reverend Richards' church and speaks with Larry.Larry confesses that the entire affair was an accident and that he never intended on hurting anyone. The guilt that has been eating at him is the reason he attempted suicide. Speedfreek enters the church and tries to kill Larry. Regardless of Larry's guilt, the Hulk is not going to allow Speedfreek to murder him in cold blood. The two fight one another, and Speedfreek even succeeds in tearing open the Hulk's stomach with his Adamantium blades. Speedfreek runs off to finish his work, but the Hulk catches up to him and hurls a car battery at him. The battery acid splashes across Speedfreek burning his exposed flesh. Screaming in pain, Speedfreek takes off. Larry is grateful to the Hulk and asks how he can repay him. The Hulk, feeling very little sympathy at this moment, tells him to go to Hell. 
Speedfreek was also one of the villains that escaped from The Raft prison. Hiding in Stamford with some other escaped convicts, he was eventually tracked down by the New Warriors, who battled with him and his friends as part of a reality show. Nitro used his powers to destroy the entire neighborhood, causing both the death of hundreds of people, the New Warriors, and presumably Speedfreek as well.
Speedfreek Suit: Joss wears a battlesuit that allows him to hover above the ground and fly at extreme speed using the boot jets. Weapons include arm-mounted adamantium cutting blades and adamantium projectile barbs. The suit can also generate a holographic image.