The X-Men is one of the most iconic superhero groups in comic book history. While more fans seem to be gravitating towards The Avengers, thanks mostly to the Marvel Cinematic Universe, the X-Men have maintained the highest quality of storytelling for decades. Also, unlike The Avengers -- who have let in and accepted just about everyone in the Marvel Universe for membership through the past few decades -- The X-Men have been pretty strict on who gets onto the team and who doesn't. Of course, there are places for mutants that don't make the cut -- such as the New Mutants, X-Force and X-Factor. However, the X-Men is a pretty elite superhero team and the membership has always been top notch.

With that said, there are also former X-Men members that people seem to forget about. These include heroes and villains, mutants and non-mutants, and even those characters that the team itself forgot ever joined their ranks. These also include some huge names in the Marvel Universe and some names that have since been forgotten by all but the most hardcore comic book readers. The X-Men have been around for 55 years now, and not all the members of this illustrious school of mutants have stood the test of time. While everyone thinks about Wolverine, Cyclops, Gambit and Rogue, there are other members of the X-Men -- heroes and villains -- that many comic book fans might have forgotten about.

15 JUGGERNAUT

Everyone knows about the Juggernaut. However, when X-Men fans are talking about Cain Marko, they think about the unstoppable villain -- the brother of Charles Xavier who held a grudge and never stopped trying to make life hell for the entire X-Men team. He wasn't even a mutant, getting his powers from a glowing ruby with mystical powers that gave Cain unlimited strength, durability and stamina.

In the movies, Juggernaut was a villain in X-Men: The Last Stand and then again in Deadpool 2. However, in 2001, Juggernaut joined the X-Men in X-Men Forever, a series where he teamed with Jean Grey, Iceman, Mystique and Toad to save the world. He remained a good guy for a number of years, a member of the X-Men, Excalibur and the Thunderbolts.

14 DARK BEAST

When it comes to the world within the "Age of Apocalypse" arc, even the most loveable characters took on sinister turns. While Hank McCoy's Beast is one of the most loyal members of the X-Men (despite questionable decisions here and there), his Apocalypse version is one of the most despicable characters from that world. On Earth-295, Henry McCoy was a genius -- like his mainstream counterpart -- but he was also a little off the rails.

In his attempts to take over and conquer the mainstream Marvel Universe, in X-Men Unlimited #10, Dark Beast altered his appearance to look like the Earth-616 Beast. He attacked and captured him, and then took his place as a member of the X-Men, working with the team on various missions. This lasted for six months worth of comics before his true nature was revealed and he fell in defeat in X-Factor #126.

13 MAGGOTT

Maggott was -- an unusual member of the X-Men, to say the least. His story started as a child, where he considered drastic thoughts when doctors told him he had cancer and he didn't want to burden his family. Magneto showed up, stopped him, and revealed the stomach pains were two slugs living in his belly. While Maggott refused to join Magneto that day, he sought him out later.

He ended up finding Joseph -- the clone of Magneto -- and thought he had found the real deal. When Maggott used one of his slugs to protect the X-Men from a bomb, they asked him to join in X-Men Vol. 2 #70. Nine issues later, he moved on to Generation X and after five issues he was gone completely. Four years later, he was part of the Weapon X storyline and was one of the first mutants they eliminated.

12 LIFEGUARD AND SLIPSTREAM

Lifeguard and Slipstream were a brother and sister duo from Austrailia -- Heather a lifeguard and Davis a surfer. When Storm and Thunderbird saved them from an attack, Lifeguard discovered she was a mutant and joined the X-Men in X-Treme X-Men #6. Soon, Davis learned he was a mutant as well and also joined up with the team.

Things did not last for the two. It turned out that Heather was also of the Shi'ar race and when her appearance changed, her brother rejected her. Slipstream left and refused to return, causing his sister and the new Thunderbird to head out in search of him. Slipstream was depowered on M-Day and Lifeguard was still a member of the X-Men -- part of the street team in Utopia -- but ended up just disappearing from the pages of the comics.

11 XORN

Xorn is a mutant whose powers derive from a small star in his brain. He had to wear an iron mask to protect his head from burning off. His powers allowed him to possess the power of the star and he could fire enough electromagnetism to incinerate someone. His powers were so frightening when he was younger than he tried to take his own life before Cyclops stopped him and convinced him to join the X-Men in New X-Men Annual #2001.

Xorn eventually became a teacher for students who were bullied and ridiculed as children due to their mutant powers. However, in New X-Men #135-137, Xorn became addicted to Kick and then formed the Brotherhood, where he chose to start a war between mutants and humans. It was a sad demise as Xorn was not in control of himself at this time and fell at the hands of Wolverine as a martyr to a cause he never wanted.

10 SABRETOOTH

For most of his career, Sabretooth was Wolverine's greatest villain. The one person who could always beat Wolverine in a fight, Victor Creed was a member of the Brotherhood of Evil Mutants and showed up every year on his own to hunt down and beat Wolverine within an inch of his life, just to prove that he could do it. However, there have been a few periods of time when Sabretooth wasn't all that bad.

In X-Men Unlimited #3, the X-Men went to stop an out-of-control Sabretooth, but Professor X ordered them to bring him back to the mansion to help him. While there, he helped the X-Men on occasion, including helping rescue the Generation X mutants in the pages of Uncanny X-Men. He ended up returning to the X-Men after M-Day and joined them starting in X-Men Vol. 2 #192, which lasted until his rivalry with Wolverine caused him to leave the group again. He is now a reformed villain (thanks to the "Axis" event), and is working with X-Men and other X-teams again.

9 PETRA AND SWAY

There is a very good reason that Petra and Sway are forgotten X-Men members. They were members of the first team of New X-Men that Professor X sent to try to save his original X-Men members -- members that Professor X covered up and hid the existence from after they failed and perished while trying to rescue the original team. Of course, the second group of mutants that Professor X put together were finally successful.

Petra could turn coal into diamonds and Sway had the power to freeze time. That first X-Men team included Petra, Sway, Darwin and Vulcan -- and while Petra was able to bury Vulcan and Darwin to save their lives, she and Sway fell in battle. This remained hidden for many years until X-Men: Deadly Genesis.

8 DAZZLER

When Dazzler first debuted in Marvel Comics, she was nothing more than a gimmick character. Marvel introduced her when its higher ups wanted to partner with Casablanca to create a new hero. The idea was for Marvel to create the character and Casablanca would introduce a singer that would portray her in real life.

From those beginnings, Dazzler wasn't much of a character in the start. After years of being unable to succeed in the music industry after the world learned she was a mutant, Alison went to Professor X for help in Dazzler #38 and she finally joined the X-Men in Uncanny X-Men #214, which lasted for two years worth of comic books. Over the years, Dazzler came and went as a part-time member of various X-teams.

7 SPIDER-MAN

Possibly the most surprising pseudo-member of the X-Men is non-mutant Spider-Man. If Wolverine can be a member of The Avengers, why can't Spidey be part of the X-Men? Of course, this partnership was not so much as a full-fledged member of the superhero team, but instead a member of staff at the school for gifted youngsters.

This happened back in 2014 when Peter Parker agreed to take on the role of a special guidance counselor at the Jean Grey School of Higher Learning. In actual fact, in Spider-Man & The X-Men #1, Peter was sent as a spy to investigate Wolverine's belief that one of the students was not who they seemed to be, but he also became a strong influence on the kids at the same time.

6 THUNDERBIRD

When Professor X recruited the New X-Men to go and save his beloved original students, he put together an amazing team. Storm, Colossus, Wolverine and Nightcrawler were among the recruits -- along with Sunfire and Thunderbird. After their first mission -- saving the original X-Men -- Sunfire quit the team to return to his home country, but Thunderbird remained on as one of the new members of the X-Men.

In the very next mission after the All-New X-Men formed, Thunderbird ignored a direct order from Professor X to prove he was a valiant warrior and ended up perishing in a plane explosion while battling Count Nefario. Years later, John Proudstar's brother took on the Thunderbird role seeking revenge against the X-Men but soon became a hero in his own right as Warpath -- helping everyone forget about Thunderbird's small role in the mutant superteam.

5 FORGETMENOT

If there is any forgotten member of the X-Men that has to be included on a list like this, it would have to be the hero known as ForgetMeNot. In an amazing bit of trivia, ForgetMeNot joined the X-Men right before M-Day, but thanks to his mutant powers, none of the X-Men or even Marvel Comic book fans had any memory of him being part of the team at all.

See, ForgetMeNot had the mutant powers causing everyone to instantly forget him once he is out of eyesight, with all memories of his existence disappearing completely. Even Professor X had to set a reminder to remember ForgetMeNot every hour or he would also forget him. While his most memorable moments came with X-Force, he was the most forgotten member of the X-Men for years.

4 CAPTAIN MARVEL

Captain Marvel is set to be the next major hero in the Marvel Cinematic Universe. However, she has been around for many years in Marvel Comics, starting out as Ms. Marvel -- a member of The Avengers -- and later becoming Captain Marvel, one of the most powerful heroes in the entire Marvel Universe.

However, there was a very dark time in her life when she battled Rogue and the then-evil mutant absorbed so much of her powers that it left Danvers powerless with most of her memories gone. Professor X took her in and helped her retain those memories. While she remained with the X-Men and aided them on their adventures, she refused official membership to the team, remaining an honorary member.

3 CLOAK AND DAGGER

Cloak and Dagger joined forces as teenagers, mostly to protect each other from a hostile world. The two were runaways and were perfect compliments, with Tyrone possessing the power of darkness and Tandy possessing the power of light. With Tyrone always in danger of turning completely to the darkness, Tandy was the only being who could keep him from slipping into pure evil.

Early in their careers, Cloak and Dagger became friends with the New Mutants, helping them on adventures, and learning that they were also mutants. Many years later, Norman Osborn brought Cloak and Dagger into his Dark X-Men group, but it was all a plan by Cyclops. After their victory, he welcomed them into the mutant community in Dark Avengers #8.

2 NAMOR

Namor, the Sub-Mariner is not, and has never been a team player. Despite that, he has been member of The Invaders, Defenders, Illuminati, Avengers, Fantastic Four -- and yes -- the X-Men. As a matter of fact, Namor has been a member of the Red Team and the regular X-Men, not to mention Norman Osborn's Dark X-Men team over his career.

Namor had a connection to the X-Men since the start, battling them alongside Magneto but refusing to join the Brotherhood of Evil Mutants. The Hellfire Club also wanted Namor to join them, an offer he also refused. After many years, Namor agreed to join Magneto and the X-Men in Utopia to help save scattered Atlanteans, and later he fought on the X-Men's side in Avengers vs. X-Men.

1 MAGNETO

Easily the greatest villain in X-Men history is Magneto. However, while Magneto made life hell for Professor X for years, he has also been a member -- and even a leader -- of the X-Men on more than one occasion. In Uncanny X-Men #200, Magneto agreed to stand trial for his crimes. After an attack almost ended Professor X, he asked Magneto to replace him as the leader and he agreed, joining the X-Men and becoming the teacher for the New Mutants.

Magneto returned years later to the X-Men to take the side of the mutants in their battle with the Avengers. When Cyclops escaped from prison, Magneto joined him as part of the new mutant liberation and was part of Scott and Emma's new school for mutants.