Since their debut in 1963, the X-Men have had dozens and dozens of mutant members (and even a few human ones, too). If you were born with an X-Gene in the Marvel Universe, odds are you've served as a member of the X-Men at one time or another. As time has progressed and multiple teams of X-Men started operating at one time, more and more mutants could claim that they, too, were an X-Man.

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Still, there are some mutants that have only served in one of the X-Men's satellite teams (X-Force, X-Factor, the New Mutants), have never graduated from being a student to the senior team, or have just steered clear of other mutants completely. Here are 15 mutants who have never joined the X-Men.

15 CALLISTO

A mutant gifted with enhanced senses, Callisto first encountered the X-Men during her tenure as the leader of the underground mutant community known as the Morlocks. While Callisto was at first an adversary of Storm and the X-Men, she later became a trusted ally of the team. She even served as Moira MacTaggert's bodyguard for a stretch of time when the X-Men were presumed dead. She also struck up an unlikely -- and mostly off-panel -- romance with Colossus, and later used her skills as a leader to assist Professor X and Magneto with rebuilding Genosha following Cassandra Nova's massive Sentinel attack on the island.

Despite acting as both an ally and enemy of the X-Men for over 30 years, Callisto has still never found herself on an official team roster. Even if she did journey out of the sewers to serve with the X-Men, she'd eventually find herself back underground with the Morlocks.

14 LILA CHENEY

Lila Cheney is a solo act. This planet-hopping rock star uses her musical talent to rock audiences all across the cosmos, and she uses her intergalactic teleportation powers to pull off impressive heists. Lila's long been an ally (as well as a frequent entertainer) of the X-Men, but she's never served as a member of the team -- or any mutant team. That's really a feat considering that her bodyguard Strong Guy and bandmate Dazzler were both frequent members of X-Men teams.

The closest Lila's come to joining any X-Team was back in the early '90s when she got caught up in a skirmish with S.H.I.E.L.D. alongside X-Force. Cheney helped the team in the battle, but then teleported out as soon as her services were no longer needed. As afraid of longterm relationships as Lila Cheney may be, though, that didn't keep her from performing a cover of U2's "One" at Cyclops and Jean Grey's wedding.

13 MANIFOLD

To date, the teleporter named Eden Fesi has yet to have prolonged contact with the X-Men, despite being a mutant. While he trained in the Australian Outback as the protege of the X-Men's close associate Gateway, Manifold's superhero trajectory was aimed at a different target: the Avengers. Fesi began his superhero career as a member of Nick Fury's Secret Warriors. This experience eventually led him to join a sprawling Avengers roster, where his highly precise and powerful teleportation powers proved useful.

While Eden Fesi always seemed to prefer a rock and roll lifestyle to a superhero one, he's managed to jump from one super-group to another. Most recently he's been spotted as a member of Black Panther's Crew; in fact, he'll officially be a part of a new "Black Panther and the Crew" ongoing series. Still, he's managed to avoid joining the X-Men, even though teleporters are always great to have on a team.

12 ABIGAIL BRAND

Super-spy and former S.W.O.R.D. director Abigail Brand doesn't like to talk about herself or her abilities. In fact, her mutant origin comes up so infrequently in the comics that you may not even know that she's not human. The child of an extraterrestrial father and a mutant mother, Brand has inherited a number of physical traits and powers that mark her as a mutant.

Her hair is naturally green, the same color as her father's fur. Her mutant ability, which she rarely displays, allows her to generate colorful flames from her hands. She's also shown that she can morph her tongue into various shapes that allow her to speak in almost any alien language. While Brand has fought alongside the X-Men, like in Joss Whedon's "Astonishing X-Men" run, she's yet to officially join the team. She prefers to keep her distance and stay in managerial positions, like her current gig in Captain Marvel's Alpha Flight.

11 QUENTIN QUIRE

Just because Quentin Quire hasn't officially become an X-Man yet doesn't mean he hasn't caused plenty of drama and headaches for the senior team. Since he debuted during Grant Morrison and Frank Quitely's "New X-Men" run well over a decade ago, Quire has been stuck as an X-Man-in-training. He's gone on missions with the team (to near calamitous effect) and made quite a name for himself, though -- which is probably why he hasn't gotten a diploma yet.

After all, the self-styled Kid Omega began his association with the X-Men by using his dangerous telepathy to whip up a riot on the Xavier School campus. His relatively good deeds in recent years have only started to make up for his deadly introduction to Xavier's faculty. Quire's also not joining the X-Men anytime soon; in the new "Generation X" series arriving this April, he'll be a member of the school's new class of misfits.

10 SHATTERSTAR

As the most '90s X-character to ever exist, Shatterstar's true origin was just revealed a few years ago -- and it's intentionally confusing. To sum up, Shatterstar is both the "father" and son of the X-Man Longshot. Shatterstar is considered to be a mutant because while Longshot himself isn't one, Shatterstar's mother (Dazzler) is. Shatterstar also possesses a few mutant powers that aren't common amongst Mojoworld natives like his father. 'Star can channel shock blasts through his swords, although he rarely uses that power because it drains him of energy. Later in life, he developed the ability to open up teleportation portals.

Shatterstar made his big debut as a member of Cable's original X-Force team, a team he served with for many years. After taking a leave of absence from superheroics, 'Star returned and joined Madrox's X-Factor Investigations. He remained a member of that organization until its dissolution and is currently missing in action. Shatterstar has still never served as an X-Man.

9 DAKEN

Perhaps the main thing keeping Daken out of the X-Men is family drama. Daken is the son of Wolverine and the X-Man's late wife Itsu, and that familial tie has led to a lot of in-fighting. Despite their deep distrust of each other, this father and son are a lot alike; they're both clawed warriors with healing factors and bad attitudes.

Pretty much every team Daken has joined has been an act of rebellion against his father. He was a member of Norman Osborn's Dark Avengers and Dark X-Men, and he later joined an incarnation of the Brotherhood of Evil Mutants. Wolverine drowned Daken during a clash between his X-Force squad and the Brotherhood, but Daken was later resurrected as one of the Apocalypse Twins' Horsemen of Death. Daken's whereabouts following the death of his father remain unknown. With Wolverine dead, there's never been a better time for his kid to join the X-Men.

8 RICTOR

Rictor's superhero career, which spans three decades, has solely existed on the periphery of the X-Men. Gifted with the power to control vibratory shockwaves, Rictor was initially rescued by the original X-Factor squad and placed in a training program with their other wards. That group of teens eventually hooked up with the New Mutants, forming the teen team that would soon morph into X-Force.

After spending a short time away, Rictor briefly rejoined his friends in X-Force -- and then took an extended leave of absence from all super-teams, alongside his partner, Shatterstar. Rictor returned to action as an original member of Jamie Madrox's X-Factor Investigations, where he would stay throughout the duration of the team's existence. While many of his teammates (like Boom Boom, Warpath, Cannonball, Sunspot and Karma) spent that time period joining the X-Men, Rictor stayed with Madrox (and Shatterstar, who would return and join X-Factor as well).

7 STRONG GUY

Like his former employer Lila Cheney, Strong Guy has yet to serve as an X-Man. Unlike Lila, Guido Carosella has demonstrated the ability to work well with others. Guido got his start as Cheney's bodyguard, a role he filled throughout Lila's '80s appearances, until he struck out on his own and joined the government-sponsored X-Factor team. Guido became that team's strong guy, since every superhero team has to have a strong guy. To his leader Havok's embarrassment, Guido chose "Strong Guy" as his codename.

Years after the government X-Factor team disbanded, Strong Guy returned as a member of X-Factor Investigations. That's it, though; if a team's named X-Factor, Strong Guy will join it. Otherwise? Apparently not. Guido has recently resurfaced in a non-speaking cameo role in the current "IvX" mini-series. While he's fighting alongside the X-Men, it's yet to be seen if that means he's going to join the X-Men.

6 SIRYN

A second generation superhero, Siryn has brought her experience and power to a number of X-Men affiliate teams over the past three decades. With powers nearly identical to those of her father Banshee, Theresa Cassidy originally fought alongside her criminal uncle Black Tom and his partner, the Juggernaut. Siryn eventually went straight and relocated to Muir Island, where she assisted Moira MacTaggert and her mutant research facility.

Siryn briefly served as a member of the Muir Island X-Men, an offshoot of the main team made up of a random assortment of mutants and superhumans. Like more than a few other members of this list, Siryn's two notable teams are Cable's original X-Force unit and Madrox's X-Factor Investigations. Terry clocked a massive amount of hours with both teams, serving with each of them for lengthy stints of time. Siryn's currently a member of no team, as she's transcended into the godly role of The Morrigan.

5 MULTIPLE MAN

You've already read this guy's name a number of times on this list so far, so Madrox's inclusion should come as no surprise. Still, it is a bit surprising, considering that the guy's been around for over 40 years. Madrox (and his many self-generated duplicates) have provided an army of members for a number of teams, but never as a member of the X-Men.

Interestingly, Madrox was originally recruited by Professor X himself. Instead of joining the X-Men in the '70s, however, Madrox went to Muir Island and became one of Moira MacTaggert's first lab assistants. Madrox stayed on Muir Island for years, with one of his dupes becoming a member of the splinter Muir Island X-Men. Multiple Man eventually joined the X-Factors: the government-funded one and his own detective agency one. Madrox's chances of becoming a legit X-Man have decreased, though, as he recently died in the "Death of X" limited series.

4 JUSTICE

Like Madrox, Justice is another mutant hero that debuted in 1975 and has still yet to serve on an X-Men team. Unlike Madrox, Vance Astrovik has never been a member of any X-Team. This telekinetic originally operated under the code name Marvel Boy and made a splash on the scene as a member of the New Warriors. After a stint in jail, Marvel Boy re-emerged under the name Justice, a moniker he's kept ever since.

Since becoming Justice, Vance has been a member of the Avengers, a few more New Warriors rosters, the Avengers Initiative, the Avengers Academy and a frequent partner (both in love and crime-fighting) of Firestar. Speaking of Firestar, she finally joined the X-Men a few years ago in the pages of "Amazing X-Men." This means that Justice is one of the most prominent Marvel mutants to never serve with the X-Men or any of their affiliated teams.

3 WOLFSBANE

The New Mutants were the first X-Men spinoff team. Originally X-Men-in-training, many of the team's members have gone on to join the X-Men. Four of the team's original members have all become X-Men. Cannonball was the first, Dani Moonstar acted as a reserve member, Sunspot joined Cannonball's hand-picked team of X-Men and Karma joined an X-Men squad in "Astonishing X-Men." The lycanthropic mutant Wolfsbane is the only original New Mutant to have never joined the X-Men.

Rahne Sinclair stuck with the New Mutants throughout the '80s and made the jump to X-Factor in 1991. She followed that up with a stint in Excalibur and a brief tenure as a teacher at the Xavier School. In the '00s, she alternated between Madrox's X-Factor Investigations and Wolverine's black ops X-Force crew -- but she never joined the X-Men proper. Like many of her X-Factor teammates, Wolfsbane's current whereabouts are unknown. Could she resurface as an X-Man, or could she join Cannonball and Sunspot in the Avengers?

2 FRANKLIN RICHARDS

Despite debuting almost 50 years ago, the powerful, reality-altering mutant named Franklin Richards is still a pre-teen -- and he's still never joined the X-Men. That may be because Franklin already has a superhero team closer to his heart. As the son of the Fantastic Four's Mister Fantastic and Invisible Woman, Franklin Richards was born a member of a superhero team and hasn't had the need to look for inclusion elsewhere.

Still, Franklin did come in close contact with the X-Men in the wake of 1996's "Onslaught" event. With his family presumed dead, Richards became a ward of Generation X and briefly attended that mutant school. When his parents came back from the alternate pocket dimension Franklin willed into existence to keep them from dying (comics!), the kid reunited with them. Since then he's stayed by their side, having adventures with the FF and the other kids enrolled in the team's Future Foundation.

1 GREAT LAKES AVENGERS

Plenty of characters have gained or lost a mutant identity over the years, usually in an attempt to make the character more marketable. Falcon was briefly a mutant, Cloak and Dagger are sometimes mutants, and Namor was retconned into being Marvel's first mutant in the early '90s. Even Squirrel Girl was originally a mutant until recently when she was revealed to be a human mutate (it's a whole other thing).

Similarly, the comedic Great Lakes Avengers team jumped on the bandwagon in the '00s when team members Mister Immortal, Big Bertha, Flatman and Doorma all realized that they were mutants. The team briefly rebranded themselves as GLX -- the Great Lakes X-Men -- and tried to ride the coattails of the headlining X-Team. The real X-Men didn't really like their signature letter being co-opted by strangers, and they dissuaded the Great Lakes team from using the GLX name. The team's core quartet is once again known as the Great Lakes Avengers, and none of them have ever served as a for-real X-Man.

Which Marvel mutant would you like to see join the X-Men? Let us know in the comments!