Once an extremely gifted scientist, Keith Kilham was onto the breakthrough of a life time. He was close to finding a cure for the world's most deadliest viruses, The Legacy Virus.
One day while he was working, terrorists attacked the lab he was working in. A bomb was set off, and the deadly virus Kilham was containing at the time escaped. Locked in his lab with the virus, in a desperate act for survival, he injected all of the anti-virus serums he could find into his body.
Days later he was recovered, but was in a fragile state. He was still alive, but his bodly tissue was breaking down and his body mutated into a dangerous state. Because of his unique state, he caught the eye of Niles Van Roekel.
After being taken by Roekel, Kilham was given an alien upgrade to control his condition, the result of which turned him into Hazmat. He would soon join The Imperfects during the invasion of Earth.
During the invasion, Hazmat bumped into Venom, who stole some of Roekel's alien tech earlier from another Imperfect member and used it in a lost battle with Spider-Man. Venom thought to get a piece of Roekel's alien technology from Hazmat.
After a battle in Grand Central Station, Hazmat defeated Venom.
Hazmat later fought Spider-Man on the Brooklyn Bridge, but lost.
At the near end of the Imperfect Invasion he was sent to find the super being Paragon, but would end up confronting Magneto, who was also seeking Paragon. Though Hazmat blinded Magneto at the beginning of the battle, he was still no match for Magneto and was defeated in Grand Central Station.
Hazmat's current whereabouts are unknown but he is still supposed to be a member of the Imperfects under the rule of Paragon. He might be off trying to find a cure for his poisonous condition.
Though the virus Hazmat was infected with was never actually identified, due to the fact that it was associated with mutant research many have come to the conclusion Hazmat was infected with a mutated strain of the Legacy Virus.
Hazmat was accidentally depicted in Marvel Universe vs. Avengers in place of Hazmat from Avengers Academy. This was actually a very welcome mistake as it has opened the possibility of The Imperfects becoming part of mainstream Marvel.