X-Men #1 became the biggest selling comic book of all time in 1991, selling 8 million copies. The book, written by longtime X-Men writer Chris Claremont and artist Jim Lee, established two separate X-Men squads, the Blue and Gold teams. Sadly, it was around this era that the Chris Claremont golden era was winding down, but Blue and Gold still produced some wonderful moments, largely because the team mixes were among the best of all time.

With some X-Men on Muir Island, others in Shiar space, Genosha on board, and threats from the Reavers, Sinister, and Shadow King, X-Factor and the X-Men reunited, albeit in two teams. In some ways, this was the beginning of the end of the X-golden Men's age. While several titles were already on the stands, Gold and Blue shattered the concept of several teams, and the team hasn't had a strong sense of cohesion since. Claremont's voice was also fading, which was the most tragic aspect of all. Despite this, the two strong teams marked a watershed moment in which fans got to see two incredible lineups at the same time.

Publisher: Marvel Comics
First appearance: "X-Men" #1

All New X-Men or The Original Five is the first Team of X-Men which consisted of Cyclops, Jean Grey, Iceman, Beast, and Angel. These are the five mutants that Charles Xavier put together so as to form the team. This team of international heroes began a new era f0r the X-Men franchise, which was on the verge of cancellation in the mid-'70s. It remains one of the best lineups in all of comics.

Many of the characters, including Storm and Nightcrawler, were designed by legendary artist Dave Cockrum. Initiated by Lein Wein and Dave Cockrum, Chris Claremont took over for Wein almost immediately and went on to be the X-main Men's writer and driving creative force until the early 1990s. Claremont also brought back Jean Grey, who, along with her paramour Cyclops, became a central character in his stories, resulting in the legendary Dark Phoenix Saga.

Publisher: Marvel Comics
First Appearance: All New X-men Vol 1 1

The 1960s era X-Men never really grew past two-dimensional characters and the All-New, All-Different contrivance that brought the O5 from the past to the future was a victim of Bendis-speak and ultimately unsatisfying beyond the initial gimmick. But the 1986 X-Factor series that brought the O5 back together for a series that ran adjacent to the Uncanny X-Men was a fantastic team comic. Not only were the original X-Men fully together again but this was an era when the characters grew in their personalities and interacted in bold new ways.

Furthermore, the X-Factor run had the melodrama for which Claremont-era comics were known, but 80s comics had not yet devolved into the modern comic trend of extreme decompression, in which nothing happens over the course of an issue. Instead, it featured exciting action-packed villains and storylines such as the Marauders, Four Horsemen, and others, as well as engaging character dynamics such as the Jean-Cyclops-Madelyn Pryor love triangle.

Publisher: Marvel Comics
First Appearance: X-Factor #1

Formed back in 1987 by X-Men scribe Chris Claremont and artist Alan Davis, Excalibur combined the already established Marvel UK characters Captain Britain and Meggan with American X-Men characters Shadowcat, Nightcrawler, and Rachel Summers. As a counterpart to the soap opera of Uncanny X-Men, Excalibur focused on a more light-hearted adventure with the team hopping dimensions and dealing more with outlandish, magical threats than mutant politics.

Excalibur helped revitalize Captain Britain and gave a couple of B- and C-listers a chance to shine in front of X-fans, even welcoming stranger characters and other X-vets as time passed. Following the House of X/Powers of X (opens in new tab) relaunch, a relaunched Excalibur series was one of the core titles of the X-Men line, though it recently ended to make way for Knights of X this spring.

Publisher: Marvel Comics
First Appearance: Excalibur Special Edition #1

Grant Morrison's New X-Men run demonstrated that anything and everything was possible in the X-Universe. Grant Morrison kept the roster small and tight-knit, focusing on developing and even overhauling their chosen characters. Emma Frost, a reformed villain, became the team's breakout character, with her romance with Scott Summers causing a schism between the X-Men leader and his then-wife Jean Grey.

Beast's appearance changed over time, giving rise to his more cat-like form, which lasted for over a decade. Then there was Xorn, the helmeted mutant who turned out to be Magneto in disguise, betraying the team and even killing Jean Grey (or sending her to the White Hot Room, where former Phoenix hosts are sent when they are killed). Morrison also embraced the aesthetic of the 2000 X-Men film, dressing everyone in sleek, black leather and reintroducing the concept of Xavier's School, creating characters such as Beak, Angel Salvadore, Glob Herman, Quentin Quire, and others who continue to play a role in the X-Men years later.

Publisher: Marvel Comics
First Appearance: New X-Men: Academy X #2