Kyle Gibney is a mutant who manifested a feral mutation during puberty; this mutation granted him enhanced strength and agility and an increased rate of regeneration. He also suffered from a bestial appearance, which prompted his parents to throw him out of their house. Living on the streets, he was kidnapped by the conspiratorial Secret Empire and subjected to mind- and body-altering experiments. The experiments had the consequence of making him psychologically unstable, and in particular prone to violent and animalistic behavior. During this time, he became acquainted with Dr. Valerie Cooper, a United States government official who was unaware of the Secret Empire's true nature or activities. He was freed by Wyre, the man who had unwittingly been the source for the genetic material that was used in the Empire's experiments.

Gibney (now Wild Child) was detained by the military and given over to the custody of Canada's secret Department H, who oversaw the formative Alpha Flight team. The Flight member Walter Langkowski, wanting to protect the youth from the military, placed him in the trainee team dubbed Gamma Flight. After Alpha Flight and its trainee groups were officially disbanded, Gibney was recruited to join the first Omega Flight team, who fought and were defeated by Alpha Flight twice. Afterwards, he committed a series of murders, which ended when he was captured by Wolverine after he almost killed Alpha Flight member Heather Hudson.

Wild Child was subsequently pardoned under unrevealed circumstances and given membership in the new Gamma Flight. When that team was also disbanded, he went berserk over his deprecated status and attacked Pathway, another trainee. Gamma's leader Nemesis teleported him away during a fight with Heather Hudson (then Guardian) and Wolverine. Department H would later help him overcome his psychological problems, train him in unarmed combat, and place him in Alpha Flight under the codename Weapon Omega. He eventually changed his codename to Wildheart and became romantically involved with his teammate Aurora.

His appearance eventually deteriorated back to his initial feral form, which prompted him to leave Alpha Flight and Aurora. He followed Valerie Cooper to the United States, where he joined the government operated team X-Factor. There he began a romantic relationship his teammate Shard. His feral teammate Sabretooth frequently attempted, with little success, to convince Wild Child to become a hunter and killer like himself. He remained with the team until his body began mutating towards a more feral form. He eventually degenerated to a near-mindless state and was recruited (either willingly or via brainwashing) by the new Weapon X team.

As part of his draft, Wild Child was paired with Sabretooth to try and recruit Sunfire to the program. The Japanese mutant refused and badly burned Sabretooth. When Wild Child mocked his burns Sabretooth viciously sliced through Kyle's vocal cords, making sure that he would remain mute. His past flame, Aurora, was also recruited into the team but she was not herself. After the Weapon X upgrades she became cocky and aloof, snubbing the ugly Wild Child and even engaging in a relationship with the horribly disfigured Director of the program. This became fuel for the fire when Brent Jackson attempted to undermine the authority of the Director Malcolm Colcord. Using Aurora's attitude toward him as motive, Jackson convinced Wild Child to join his splinter group, and was still seen with this group in the limited series Weapon X: Days of Future Now.