Mutant Colin McKay was seven when the crimelord Vixen had him kidnapped from his home outside Edinburgh. Escaping, he hid in a derelict factory on the shores of Loch Daemon, where, scared and lonely, he chanced upon the robotic Widget, making an instant friend. When the Vixen’s men followed, Widget sent Colin through a portal to another reality. Colin re-appeared on the ice plains of Ee’rath (Earth-148) and was taken to the exiled Royal Household of Queen Ai'sha, recently deposed by the evil mage Necrom. The benevolent witch-queen entrusted Colin to the mystic Zz'ria, who trained him as a warrior. Over the next twenty years, an increasingly leonine Colin became known as Kylun while developing his mutant talent for sound mimicry and pledging his heart to the sorceress Princess Sa'tneen, Ai'sha's daughter. Fearing the queen’s growing army, Necrom launched a surprise attack. Most were slain or captured; badly wounded, Kylun was left for dead. Recovering, he rescued Sa’tneen and they rallied an army, gradually driving the tyrant’s men back to the Dark Citadel, Necrom’s last stronghold. Penetrating this bastion, the lovers confronted Necrom, who attacked them with the zombified remains of their world’s greatest heroes, Excalibur. Sa’tneen neutralized the zombies by attacking Necrom, who killed her. She died in the arms of Kylun, who pursued the fleeing Necrom through a door, emerging in the lighthouse of Earth-616’s Excalibur team. Mistaking Nightcrawler for a demon, Kylun attacked him, but realized his mistake after his mystic blades proved unable to hurt the virtuous Nightcrawler. Widget’s arrival confirmed that Kylun had returned to his own Earth, though the time-rate differential between worlds meant only a year had passed since his departure, and that Necrom had arrived there a month earlier.
Kylun teamed with Excalibur to fight Necrom, his blades proving to be one of the few effective weapons against the mage. After Necrom’s defeat, Kylun elected to stay with the team, fighting the time-manipulating assassin Sidestep and the early X-Men (or alternate dimensional counterparts), and helping to investigate the Crazy Gang’s bizarre Wonderland. Still brooding over his lost love, Kylun returned to Scotland in search of his family, but on his parents’ doorstep, before he could ring the doorbell, he was assaulted and kidnapped by Warpie agents of R.C.X. (the Resources Control Executive). Taken to their base, Cloud Nine, he and other similarly abducted Excalibur allies were held in stasis until Nightcrawler freed them. Back with Excalibur, he helped the extra-dimensional warrior Khaos defeat the evil Ghath, traveled to Earth-811 to assist its surviving heroes in overthrowing the ruling Sentinel regime, and joined in trying to rescue his teammate Cerise after she was apprehended for war crimes by the Shi'ar.
Finally locating his parents, Kylun left Excalibur to move back in with them. He later attended the Otherworld wedding of his teammates Captain Britain (Brian Braddock) and Meggan.