BIOGRAPHY
Robert Hunter was a bitter old man who felt he never caught a break his entire life. By his senior years, his wife had passed away and he was fired from one job after another as an electrical engineer, forced into early retirement. He had some love for his daughter Virginia and her passion for art, but his life was otherwise empty. While operating a ham radio as a hobby, Robert picked up the sound of voices speaking to him through his equipment. He made the mistake of telling Virginia, and his daughter tried to have him committed. The voices were real, though, and they offered him power. [Peter Parker, the Spectacular Spider-Man (1st series) #55]
The Lunatic Legion was a group of Kree officers, operating from the Blue Area of Earth’s Moon. They chose Robert Hunter to be one of their agents and imbued him with great power by 
exchanging the gluon particles of his atoms with psion particles. This change allowed Robert to release the stored energy of his mass at will, exploding with violent force. The psions could then gravitate back together, reassembling his body from a hazy mist of living particles. With this newfound ability, Robert could take revenge on the society that he hated. He became Nitro, the Exploding Man, and eagerly (if belligerently) entered into the service of his new masters.
The Lunatic Legion sent Nitro to Gary, Indiana, to retrieve Compound-13, a cataclysmically deadly nerve gas being transported under guard by the Air Force. Nitro brazenly forced his way into the 
midst of the security team led by Carol Danvers before detonating with a force that leveled all opposition. He commandeered the armored car transport and sped off with his prize. By happenstance, Nitro struck another vehicle carrying the traveling singer Rick Jones, who used the Nega Bands on his wrists to summon his counterpart, Captain Marvel. Even the cosmically aware Mar-Vell wasn’t fully prepared for Nitro’s power, and the villain escaped while Mar-Vell was riding out the shockwave of his latest blast.
After Carol Danvers caught up with Mar-Vell and explained the dangers of Nitro’s stolen property, 
Captain Marvel pursued the fiend. Nitro’s constant exploding had dire consequences when the Compound-13 pressurized canister sprung a leak, spraying deadly nerve gas into the air. Working on borrowed time, Captain Marvel changed back into Rick Jones and guided his partner in a brief struggle with Nitro. At the moment Nitro next exploded, Mar-Vell signaled Rick to trigger their own explosive transformation. Nitro’s power, combined with the photonic surge of the Nega Bands, scattered Robert Hunter’s atoms far farther than the psions could reassemble him, ending his threat. Captain Marvel then made his way to the canister and sealed the Compound-13 before more could escape. [Captain Marvel (1st series) #34]
Nitro was not dead, however, but merely dispersed. In time, his particles eventually found each other and reassembled in New York. Fixated on revenge, Nitro struck out at the red-and-blue costumed mystery hero called Omega before he realized it wasn’t Captain Marvel. Nitro continued on an explosive rampage in the city, trying to draw the attention of Captain Marvel and his 
Avenger friends by wrecking a Stark International plant. Omega pursued Nitro and made a plan to contain his blast. Stark International manufactured engine components designed for space shuttles, able to weather intense heat and force. By slamming one of these hollow tubes on Nitro before he exploded, Omega effectively turned it into a gun barrel, containing any damage to the surrounding area and instead blasting Nitro’s atoms straight up into the stratosphere. [Omega the Unknown #8]
Nitro’s metabolism was effectively in stasis whenever he wasn’t in human form. Inevitably, his 
atoms slowly gravitated together and found one another again. Still fixated on revenge, Nitro reassembled himself and immediately went after Captain Marvel once more. Nitro had evolved into a dangerous, hand-to-hand fighter, using his powers to explode only his fists for a deadly blow that reformed faster than his whole body. By this point, Mar-Vell and Rick had separated, leaving Captain Marvel unable to pull the same trick twice. Instead, Captain Marvel caught Nitro in his most vulnerable state, post-explosion. Using a ruptured tanker truck melted to the ground by bubbling tar, Mar-Vell created an air-tight seal that trapped a portion of Nitro’s mass inside the tank while leaving half outside of it. The purplish dispersed mist of Nitro’s body could not reform itself, leaving him helpless. [Captain Marvel (1st series) #54]
At Captain Marvel’s direction, the authorities managed to capture Nitro within two mobile canisters to prevent him from reforming. Robert Hunter faced numerous local and federal charges, and he was turned over to the Department of Energy’s Project: P.E.G.A.S.U.S. pending trial. P.E.G.A.S.U.S. (Potential Energy Group, Alternative Sources, United States) had a standing agreement with the 
government to study the unique powers and energy emissions of different “super-villains.” However, when Virginia Hunter learned of her father’s situation, she hired an attorney named Emerson Bale to defend his rights. Bale argued that Robert Hunter had not been convicted of any crime, yet he was being used as a test subject for experiments against his will. He produced a court order demanding that P.E.G.A.S.U.S. turn Mr. Hunter over to his daughter, pending his court date. When Bale learned his client was being kept physically separated in a pair of pressurized tanks, he immediately objected to this cruel and unusual punishment. Once Director Wilburn opened the canisters and let Nitro reform, however, Robert Hunter immediately escaped custody with Virginia and Bale as his prisoners. Robert still loved his daughter, but he had little patience for her after the attempted commitment.
While knocking over a bank as Nitro, he drew the attention of the nearby Spider-Man. Peter Parker got creative trying to stop Nitro once he realized how his powers worked. First, he started web-slinging with a snared Hunter like a pendulum, keeping him from focusing enough to explode. He brought them to Chemico and webbed Nitro to a real pile of nitroglycerine, hoping he wouldn’t risk the blast. Nitro did, though, and even the extra burst from the nitroglycerine wasn’t enough to fully disperse his molecules as they had in the past. Switching tactics, Spider-Man spotted a canister of nausea gas used during riots, known for chemically bonding well with other gases. Spidey webbed a canister of the gas to Nitro so that, the next time Hunter exploded and reformed, he inadvertently bonded the nausea gas with his own molecular structure. Violently ill at an atomic level, Nitro was no further trouble for the authorities. [Peter Parker, the Spectacular Spider-Man (1st series) #55]
Extra effort was made in the future to keep Nitro under control while in custody. He spent some time in Bellevue Hospital, purging the nausea gas out of his system, held in a tent of inert gas to prevent the ignition necessary for his explosions to work. [Peter Parker, the Spectacular Spider-Man (1st series) #56] Emerson Bale would no longer defend a client who kidnapped and tried to kill him, and Project: P.E.G.A.S.U.S. soon regained custody of the Exploding Man. Security Chief Quasar oversaw Nitro’s transport out of Manhattan to upstate New York. Nitro was kept in a medically induced coma for the duration to ensure there was no trouble. [Marvel Team-Up (1st series) #113]
Nitro’s day in court finally came, but apparently he found less diligent representation that Emerson Bale. Robert Hunter was held inside a canister of nausea gas to neutralize his threat during the trial. The Vulture and Tinkerer attempted to arrange Nitro’s escape, but they were opposed by the mutants Rusty Collins and Skids. After the Tinkerer’s device freed Nitro and cleared his head, Robert Hunter showed no gratitude towards his saviors. Instead, Nitro prepared to make his biggest explosion yet to destroy the courthouse and everyone in range. Skids jumped him at the last moment, wrapping him in her force field bubble and containing enough power to destroy a city block. Skids was too weak to try again as Nitro reformed, but she needn’t have worried. The backlash from exploding in too confined of a space left Nitro’s molecular bonds unstable. He dispersed harmlessly into atoms without being able to hold himself together long enough to explode again. [New Mutants (1st series) #86]
Nitro apparently ended up back in custody at the Vault, but interested parties managed to arrange his release. His benefactor’s representative Hardcore gathered a team called the Untouchables with Nitro, Tombstone and Kickback. They were interested in private investigator Dakota North and the background research she did on Luke Cage for the Chicago Spectator. Nitro announced their intentions by blowing up in the lobby of the Spectator when they couldn’t find Dakota directly. 
Next, they forced Dakota’s employee Teague to call her in to the office. Nitro and the Untouchables fought with Luke Cage and also dealt with the arrival of his ally, the Punisher. However, Nitro’s lack of professionalism began to grate on his partners, and they started to suspect his long periods of being drugged while in custody left him genuinely unstable. While escaping in a van with the kidnapped Dakota, Kickback shoved Nitro out of the vehicle and left him to deal with Cage. [Cage (1st series) #2-4]
Nitro was next hired by Thanos of Titan, along with Rhino, Titanium Man, the Super-Skrull and Geatar. With the promise of riches and his intimidating manner, Thanos pressed his recruits to travel to the planet H’aarg and retrieve the Oracle of Ancient Knowledge, a messiah figure intent 
on starting a religious war in the cosmos which threatened his plans. Thanos inevitably betrayed his lackeys and they were left adrift in space after escaping the monks. Their escape pod’s distress signal was picked up by the Silver Surfer and Legacy, son of Mar-Vell. Nitro was astute enough to recognize who Genis’s father must be. Nitro also knew he was responsible for Captain Marvel’s death by cancer from exposure to Compound-13 in their first encounter. His vicious sense of humor led him to shake Legacy’s hand and laugh at the clueless boy behind his back. [Secret Defenders #12-14]
Legacy eventually got the joke and pursued Nitro to take revenge for his father’s demise. Nitro had taken off for Hala, homeworld of the Kree, after their rescue, perhaps hoping to reconnect with elements of the Lunatic Legion. When Legacy caught up to him, Nitro and Genis fought in the 
ruins of the Kree Empire caused by the fallout from the Nega-Bomb. Nitro laughed at the kid as they traded blows but eventually Genis started to get the upper hand. Their fight carried them into a military museum, where Legacy beat down Nitro and was prepared to finish him. Only seeing a quote from Mar-Vell on the wall stopped Genis from murdering Nitro in cold blood. Instead, he apprehended the villain and brought him back to Titan for imprisonment. [Cosmic Powers #4]