Jonothon Starsmore and his girlfriend Gayle Edgerton were at a London nightclub when his mutant ability erupted in an explosion of psionic energy. The blast tore a hole in his body from his mouth to his navel, destroying several of his major internal organs including his heart and lungs, and also crippled Gayle’s legs. Jono survived the manifestation, though his body had been transformed into a “chamber” of volatile energy. Horrified, Jono fled. Denied a normal existence, Jono had developed a bleak outlook on life when he was invited by Charles Xavier to join the reopened Massachusetts Academy as a member of the mutant trainees Generation X. Accepting the offer, Jono arrived in the United States and was attacked at the airport by the energy vampire Emplate, who was driven off by the arrival of Chamber’s new teammates and their teachers, Banshee and Emma Frost.
Adopting the codename Chamber, Jono resided in the Academy’s basement, remaining apart from his teammates. His control over his powers suffered a setback when he accidentally destroyed the girls’ dormitory in a panic after being kissed by his then-inebriated teammate, Husk (Paige Guthrie). Jono soon began romancing Paige, and single-handedly defeated Omega Red before confronting his old flame Gayle, who sought revenge on Jono. Gayle had struck a deal with Emplate to empower her, allowing her to capture Jono while Emplate’s other recruits, whom he named his Hellions, captured the rest of Generation X excepting M, who sought aid from the X-Men’s Bishop. Emplate ultimately reneged on his deal with Gayle, holding her prisoner alongside Generation X. After Emplate was defeated, Jono and Gayle reconciled their differences.
Jono was briefly abducted by the psionic entity Onslaught, causing him trouble in focusing his powers. En route to the Xavier Institute for help, Jono and his teammate Skin were waylaid by the vigilante X-Cutioner, whom Skin defeated. After the X-Men defeated Onslaught, Jono’s focus returned, and he accompanied Paige to her family’s farm for a Thanksgiving holiday which ended with the pair’s romance breaking down. After being captured and imprisoned by Banshee’s cousin Black Tom Cassidy, the team encountered Glorian, a shaper of dreams, who granted the team their innermost desires. For Jono, it was to be whole once more; however, after Skin cast doubt on Glorian’s interpretations, the effects faded. Soon after, Jono and Paige reconciled while facing the Prime Sentinels of the government-sponsored anti-mutant Operation: Zero Tolerance.
Generation X subsequently joined an other-dimensional group of superhuman teens in opposing Emplate and Professor Pretorious. Jono, alongside Husk and Skin, then joined Spider-Man against Major Love and his Direct Euthanasia Action Division, during which Jono used his psionic powers to enhance Spider-Man’s precognitive “spider-sense” to prevent Love from massacring a crowd of innocents. Jonothan also faced the Circus of Crime, who were actually seeking to reform; Nanny and the Orphan-Maker; an alliance between Emplate and Chimera which was foiled with the aid of mutant possessor Dirt Nap; and Emma’s former business rival, Bianca LaNiege. Later, when the X-Man Psylocke was tricked by the Shadow King into releasing a telepathic pulse, Jono lost his telepathic speech, rendering him effectively mute. The effects of the pulse eventually wore off, and Jono’s speech returned just before he and his teammates faced Dracula. During the encounter, Dracula briefly restored Jono’s face and body before biting him; however, Jono’s powers seemingly allowed him to reject the vampire lord’s influence.
After the Academy began accepting human students, Jono was unhappily forced to pass as a mute burn victim. More threats followed, with Jono and his teammates battling the cyber-morph Paradox; joining former X-Men member Maggott in opposing exotic hunter Constantine Slaughter; allying with X-Man (Nate Grey) against the Dark Beast and his Gene Nation; rescuing their teacher Banshee from Hunter Brawn and his super-powered bodyguard Legault; opposing the Rising Sons in Madripoor alongside the mercenary Paladin; another battle with Emplate; resisting an attempt by Emma’s psychotic sister Adrienne to kill them; fighting alongside the New Warriors against the mutated Biohazard; facing the triple threat of Black Tom Cassidy, the Juggernaut and the mutant Mondo; and opposing Warden Coffin’s House of Correction.
Following the death of Banshee’s love Moira MacTaggert and his turning to alcohol for solace, as well as Emma’s increasingly disturbing behavior, the students left the Academy, effectively forcing the school’s closure. Jono had received an invitation from Charles Xavier to graduate to the ranks of the X-Men, which he declined, choosing instead to return to London. There, he saved teen pop sensation Sugar Kane from a mob of adoring fans and briefly romanced her before she admitted she was only using his mutant status to boost her career. Jono reconsidered Xavier’s offer and joined the X-Men, and was reunited with several of his former Generation X teammates who had joined their former teacher Banshee’s new paramilitary X-Corps unit. His fling with Sugar Kane having made headlines, Jono’s reunion with Paige was awkward at best.
At Cyclops’s request, Chamber enrolled in Empire State University’s pro-mutant program to investigate the deaths of mutant students on campus after a bombing of the co-species Students for Tolerance organization. Chamber discovered that the boyfriend of the group’s leader, Gigi Martin, had caused the blast to martyr her dead friends, thus furthering her organization’s cause. Though ESU dismantled the pro-mutant program, they retained one mutant student at the request of the Xavier Institute, who in turn took in a human student, Jono’s wheelchair-bound ESU roommate Walter. Jono sought to be taken off field duty with the X-Men to concentrate on a career in teaching; however, on returning to the Institute, he was shocked to discover that Paige had joined the team and was dating their teammate Archangel.
Soon after, Jono volunteered to infiltrate the subversive Weapon X program, using his former relationship with Husk as a means to create public dissent between himself and the X-Men and attract the attention of Weapon X director Brent Jackson. Jono was recruited into the program and, as an incentive to stay, had his face and body reconstructed with technology that was linked to his mutant energy. For his first mission, Jono was tasked with assassinating John Sublime, founder of the mutant-harvesting U-Men. Despite having reservations about killing, Jono completed his mission, seemingly solidifying Jackson’s trust in him. Soon after, Jono went missing while seeking to close down Weapon X’s secret mutant concentration camp “Neverland.”
Chamber seemingly resurfaced in Los Angeles, his face and chest once again shattered, and joined the former teen-hero support group Loners. However, it was soon revealed that a member of the criminal group the Pride was using Chamber’s identity to infiltrate the Loners and prevent them from capturing the Pride’s runaway children. Recently, following the House of M|warping of reality by the mutant Scarlet Witch, Jono was one of many mutants who were depowered after reality was restored. As a result, the Weapon X technology that had restored his face and body ceased working, leaving him in critical condition on life support. He was the subject of a focus piece by Sally Floyd, reporter for The Alternative, the first in a series of former mutants, and the column quickly became a national sensation.
Recently, however, Chamber was kidnapped from his hospital room by agents of Apocalypse, who were now working for the ages-old mutant's right-hand man, Ozymandias. It was revealed that the Starsmores were in fact descendants of Apocalypse. Chamber was transformed into a scrawny, teenaged version of Apocalypse, and was asked to join their secret society. Chamber respectfully declined. Soon afterward, he was approached by Pete Wisdom, in hopes of recruiting him to the most recent incarnation of Excalibur. This time, Starsmore angrily rebuked Wisdom.
He then joined the new team of New Warriors lead by Bandit