Robert Hunter was an retired electrical engineer who operated a ham radio as a hobby before the Lunatic Legion, a group of rebel Kree who had been monitoring his broadcasts, chose him to become their agent. The Legion took him to a hidden genetics laboratory and genetically altered his body, endowing him with the ability to explode his body's molecules and reassemble them at will. Dubbing him Nitro, they sent him to acquire Compound Thirteen, a dangerous nerve gas being developed by the U. S. Army. This led him into a direct confrontation with Captain Mar-Vell, in which he was defeated and left in a gaseous state.
After months of effort, Nitro reintegrated himself and searched for Mar-Vell in order to gain retribution. While searching for Mar-Vell, Nitro mistook the alien Omega for his enemy, and attacked him, but was defeated by Omega when a titanium steel cylinder was placed around Nitro as he exploded, causing him to be rocketed into the stratosphere.
Later, Nitro again reintegrated, and lured Mar-Vell into battle. Mar-Vell subdued him once again by capturing half of Nitro (while in his gaseous state) in a container, preventing him from physically reintegrating. This container, and a second filled with the other half of Nitro's gaseous substance, was taken to the government energy facility Project: Pegasus for study. He was later released when his daughter Virginia acquired a court order in order to permit him to stand trial. Once both of the substances were recombined, he escaped and wreaked havoc in Manhattan until Spider-Man trapped him in a container partly filled with a nausea gas. Nitro later escaped once again to resume his criminal career.
Shortly after escaping, Nitro accepted a contract from the Mandarin to battle Iron Man, but was again defeated. During the battle Iron Man detected the emission of a certain frequency before each explosion, and quickly deduced that it was what caused Nitro to explode at will. He duplicated the signal, weakened Nitro by repeated explosions which in turn knocked him out. Iron Man gave him over to S.H.I.E.L.D.. who again placed Nitro into custody, eventually ending up at the super villain facility at Ryker's Island prison. He was among the many criminals to escape during a massive super villain breakout on Ryker's Island.
Recently, he was located in Stamford, Connecticut during a televised raid of a house containing him, the Cobalt Man, Speedfreek, and Coldheart. During the battle Nitro was attacked by Namorita. After being slammed into a bus, and continuously taunted by Namorita, he let off a massive explosion that killed the majority of The New Warriors, the children at a nearby elementary school, and the residents of the surrounding neighborhood. He escaped before the aftermath was picked up by various superhero teams, and is currently being hunted by Wolverine. In the wake of the tragedy, Capitol Hill proposed the Super Hero Act, requiring all costumed heroes to unmask themselves before the government and subject themselves to federally mandated standards.