Other teams are founded, but Excalibur was forged. The machinations of Omniversal guardian Roma, following a plan prepared by her late father Merlyn, brought together X-Men Nightcrawler, Shadowcat and British heroes Captain Britain and Meggan. Nightcrawler and Shadowcat were recovering injuries that were sustained during the massacre of the mutant Morlocks by the assassins known as the Marauders. They were both hospitalized at the research base of Dr. Moira MacTaggart on Muir Isle of the coast of Scotland. Shadowcat and Nightcrawler were already acquainted with the Britian superhuman superheroes Captain Britain and his mutant companion Meggan; in fact, Captain Britian's sister, Elizabeth, had joined the X-Men under the name Psylocke. All four heroes were grieving over the apparent death of Psylocke and the rest of the X-Men in Dallas.
Back in the United States, the active members of the X-Men were killed in their battle against the powerful mystical entity called the Adversary. The guardian of the multiverse known as Roma restored the X-Men to life, but the X-Men decided to allow the rest of the world to believe they were dead, so as to avoid the persecution from which mutants suffered. The news of the X-Men's survival was kept secret even from Nightcrawler and Shadowcat, who were still on Muir Isle. The escape of Phoenix from Mojo's realm served as a catalyst to unite the five as a team, initially working together to prevent both Roma's agents the Technet and Mojo's Warwolves from recapturing his former prisoner. The group set up base in Captain Britain's lighthouse home, though from the start individual members experienced several reality slips within the structure. Elsewhere in the U.K., the mysterious, robot-like Widget was also inadvertently facilitating travel between realities; among others he sent young mutant Colin McKay to Ee'rath (Earth-148), U.F.O. hunter Rupert Holloway to Earth-794, and brought deposed tyrant Opal Lun Sat-Yr-9 to the mainstream Earth (Earth-616).
Meanwhile, Excalibur's earliest escapades saw them stop Juggernaut from escaping prison, and take on the Crazy Gang and Arcade in Murderworld. They soon made alliances with the Weird Happenings Organization, its commanding officer Brigadier Alysande Stuart and her brother, the scientist Alistaire Stuart, as well as Commander Dal Thomas of Scotland Yard; however, another of their friends, Brian's old flame Courtney Ross, was killed and replaced by Sat-Yr-9, her doppelganger. Excalibur soon clashed with Lightning Force, Nazi-counterparts of themselves who were seeking to retrieve some of Widget's other dimensionally displaced victims. While returning the Nazis to their home dimension, Widget's powers accidentally led to Excalibur and Alistaire Stuart embarking on a prolonged caper across the timelines, struggling through numerous alternate realities as they sought to find their way home. Back on Earth-616, "Courtney" used Jamie Braddock, Brian's deranged reality-warping brother, to take over the crimelord Vixen's organization, and befriended Shadowcat when she returned home ahead of the rest of the team.
Excalibur finally made it back to Earth-616 to face new foes such as Galactus, Mastermind (Jason Wyngarde), Alfie 0'Meagan, and Nightmare. Mesmero temporarily took control of their minds, using them to battle Fenris (Strucker twins), until Shadowcat returned to the fold and freed them. Reunited, Excalibur took on Arnim Zola, Silver Sable and her Outlaws, Thor, the Wrecking Crew, and, with the help of the Avengers, Dr. Doom. Nightcrawler developed feelings for Meggan, leading to tension between him and Captain Britain, which eventually erupted into a brawl. As a result, Brian was snatched by the Corps; a group composed of the various "Captain Britain"-type heroes created across the multiverse by Merlyn; as Earth-616's representative, he was taken to Othervorld and tried for breaching their rules by attacking a member of the population he was assigned to defend. The case was dropped at the request of Roma, but while there Captain Britain learned of her involvement in the creation of Excalibur, and that his lighthouse was an interdimensional energy focus stretching across the multiverse.
Meanwhile the warrior Kylun (the now adult Colin McKay) flushed Necrom, the foe Excalibur had been created to fight, from his hiding place on Ee'rath. Necrom fled back to Earth, where his preparations to awaken the life-destroying Anti-Phoenix drew the attention of Excalibur and government agency F.I.6. Necrom merged with the Anti-Phoenix, and slew most of F.I.6 before flying to the Lighthouse to attack Excalibur. There he faced both the founding members and their new allies: Kylun, who had followed him from Ee'rath; surviving F.1.6 agent Micromax; the extraterrestrial Cerise; and Feron, last in a line of mages bred for generations to face the Anti-Phoenix. While these allies battled Necrom, the Excalibur founders physically merged with one another to undo his attempt to compress the multiverse into a singularity. Once this was done, Phoenix faced Necrom alone; he was destroyed attempting to absorb all her power, but she was rendered comatose. Merlyn revealed he was still alive, but, angered at his manipulations, the team destroyed the lighthouse rather than let him use its energies. They relocated to Braddock Manor, and soon afterwards the Phoenix force removed its injured host.
Sat-Yr-9 then revealed her true colors, attacking the team and their friends, but she, Jamie Braddock, and her agents were driven off. Subsequently Excalibur teamed up with the X-Men to rescue the mutant Alchemy from the Troll Associates, fought alongside some of the Avengers in Wakanda against Icon, and Brian finally proposed to Meggan. Government agency R.C.X., the Resources Control Executive, founded to gather the superpowered victims of a reality warp which had once afflicted Britain, turning these °Warpies" into a private army, became alarmed at the rise in the number of freelance superhumans operating in the U.K., and at the sudden power loss affecting many of their Warpie agents (a result of the destruction of the lighthouse). R.C.X. tried to forcibly co-opt the services of Excalibur until the heroes managed to impose a change of leadership within the organization. Then Phoenix returned, her mind heated, to take the team to her own dystopian future, where, allied with surviving heroes of that time, they reprogrammed the ruling Sentinel regime to preserve all life. However their return from the future saw Captain Britain lost in the time stream.
Cerise subsequently returned to the Shi'ar to do penance for war crimes, Kylun left to find his parents, Micromax departed for a job in America, and Feron seemingly wandered off. It soon became clear that Phoenix and Captain Britain were somehow linked, with the missing hero's features intermittently switching places with some of Phoenix's. The team relocated to Muir Island to use that facility's equipment to try to retrieve Brian. With the help of Nightcrawler's old flame, sorceress Amanda Sefton, now calling herself Day Tripper (and later Daytripper), they rescued the lost hero, with Phoenix taking his place in the time stream. However his travels had changed him; plagued with memories of the future, Brian took the new identity of Britannic.
Excalibur went on to battle D'Spayre and Stryfe's agent Zero, and gained a new member in the techno-organic Douglock, before facing the threat of the Phalanx. Shadowcat learned the magical Soul Sword she had become bonded to when her friend Illyana Rasputin died was too dangerous for her to keep. It was capable of bringing out her dark side, and coveted by mages such as Gravemoss, so Day Tripper passed it to her mother Margali, not realizing that she would then use it to kill other sorcerers to advance her own rise to power. Former spy Pete Wisdom joined the team when Excalibur made a trip to Genosha; Wisdom and Shadowcat soon became lovers after working together to investigate his old employers, the covert ops Black Air. Not long after this both Wolfsbane and Colossus joined Excalibur. Meanwhile, as Brian gradually became his former self and abandoned his Britannic identity, he suffered one last prophetic vision, which hinted at a terrible future that would come to pass if Black Air and their allies in the London Branch of the Hellfire Club were not stopped. Brian used his family connections to infiltrate the Club and resumed the role of Captain Britain. As the villains attempted to use a kidnapped Douglock combined with Margali's magic to take over Britain, Excalibur opposed them, thwarting their plans and averting the catastrophic destiny Brian had foreseen.
A short time later Brian renewed his proposal to Meggan, but before she could answer, they were attacked by the Crimson Dawn, who wanted to use Brian's powers as a key to eroding the barriers between Earth and the dimension their group had once been banished to. Aided by Excalibur, Brian and Meggan managed to stop them, but at the cost of Brian's powers. In spite of this, a few months later the pair was married in Otherworld at a wedding attended by many of their friends. Sensing the time was right, Excalibur disbanded, with many of its members returning to America and the X-Men.
A new team was briefly formed when the computer Mastermind was reprogrammed by Kang and attacked Otherworld; disguised as Roma and at the head of an army of Warpies, Mastermind slaughtered the Corps, imprisoned the real Roma, and took over the realm. With many of the Corps dead, Captain U.K. fled to Earth616 and enlisted the aid of Brian Braddock, Meggan, Psylocke, and the Black Knight. They returned to Otherworld to confront the tyrant. Brian reclaimed the powers of Captain Britain, and with the addition of Crusader X and Sir Benedict, this new Excalibur freed Roma and liberated the realm. Afterwards Roma abdicated the throne of Otherworld to Brian, who was crowned King.
Professor X and Magneto recently organized a new team in devastated Genosha, but it has no relationship with the previous teams.