X-Men - Who Is Juggernaut's Brother?

Nothing can stop the Juggernaut: This indomitable comic book supervillain has been punching and pounding his way through the Marvel Universe for over 50 years. Born Cain Marko, the Juggernaut is empowered by the mystical Crimson Gem of Cyttorak, which gives him nearly unbeatable levels of physical strength and durability. Created by the legendary Jack Kirby and Stan Lee, Juggernaut first appeared in 1965's "X-Men" (vol. 1) #12, where he attacked the first class of teenage mutant superheroes. Juggernaut has since gone head-to-helmeted-head with heroes like the Hulk, Spider-Man, Thor, and Doctor Strange, making him a brawler of epic — even cosmic — proportions.

An iconic fan-favorite comic character, the Juggernaut has crossed over into video games, cartoons, and the live-action films "X-Men: The Last Stand," "Deadpool 2," and "Deadpool & Wolverine" (played by actor Vinnie Jones, a CGI Ryan Reynolds, and bodybuilder Aaron W. Reed, respectively). But audiences who have only encountered the Juggernaut through other media may not know a key piece of Cain Marko's backstory — namely, that his brother is a major Marvel hero. Since X-Men family trees are notoriously complicated, here is a quick history of the Juggernaut's relationship with his brother.

The Juggernaut's brother is none other than Charles Xavier, aka Professor X, the founder of the X-Men. Born with the X-gene that marks him as a mutant — the next step in human evolution — Xavier is a brilliant geneticist and one of the world's most powerful telepaths. When his psychic abilities are amplified by his cybernetic helmet Cerebro, he can read and control virtually every mind on Earth.

Introduced in "X-Men" (vol.1) #1 in 1963, Professor X operates Xavier's School for Gifted Youngsters as a safe haven for mutants to control their superpowers, and his first five students (Cyclops, Marvel Girl, Iceman, Beast, and Angel) are the original X-Men. Xavier is a pacifist dedicated to his "dream" of human-mutant co-existence, but he also has a darker side, and his manipulations and machinations have occasionally estranged him from his students. More recently, Professor X establishes the mutant nation of Krakoa alongside his longtime enemy/ally Magneto in "House of X" #1.

Professor X has been ranked among the most powerful X-Men and the greatest superheroes of all time. Patrick Stewart played Xavier for over 20 years in the live-action "X-Men" films, with James McAvoy playing a younger Xavier in four prequels, and Harry Lloyd playing another version of Xavier in the tv series "Legion." He has appeared extensively in Marvel video games, novels, and cartoons, though only a few, such as "X-Men: The Animated Series" and "X-Men: Evolution," have explored his relationship with Juggernaut.

The Juggernaut is actually Professor X's stepbrother, the son of atomic researcher Kurt Marko. According to Juggernaut's origin story "X-Men" (vol. 1) #12, Kurt Marko worked alongside Charles's father, Brian Xavier, but selfishly chose not to save him from a fatal nuclear blast in New Mexico. Marko quickly romanced Charles's mother Sharon, but young Charles sensed with his blossoming psionic powers that Marko only married her for her wealth.

The relationship between Charles and his new stepbrother Cain was immediately troubled, with the short-tempered Cain resenting Charles for his academic and athletic prowess and for seemingly winning his abusive father's favor. One night, Charles stumbled on Cain fighting with his father, and Cain impulsively started a fire that consumed Kurt Marko's laboratory. In his one act of courage, Kurt died saving both boys from the burning building. This did nothing to improve their relationship: Cain became physically violent toward his stepbrother, forcing Charles to use his psychic powers to protect himself. Unfortunately, that was only the beginning of their deadly sibling rivalry.

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In a strange twist of fate, Charles and Cain both joined the army and fought side-by-side during the Korean War. (Remember, these comics were originally published in the 1960s, before Marvel's sliding timescale was in full effect.) While under attack, Cain deserted the army by fleeing into a strange cave; Charles quickly followed, warning his stepbrother that he was risking a court-martial with his cowardice.

Hidden inside the cave was the lost temple dedicated to Cyttorak, a demonic deity that had been banished from their dimension centuries earlier. Cyttorak left behind a curse so that anyone who touched the temple's gem would become a human juggernaut and act as Cyttorak's evil avatar on Earth. "X-Men" (vol.1) #12 depicts Cain's discovery of the Crimson Gem of Cyttorak: Unable to resist its sinister pull, Cain grabs it, and the mystical transformation triggers an enormous cave-in. Charles, the only witness to Cain's fate, narrowly escapes, grimly aware that if his stepbrother ever emerged from the collapsed mountain, he would now be an unstoppable force.

Juggernaut inevitably escaped, fueled by his desire to destroy his hated stepbrother once and for all. By that time, Charles had become Professor X and begun training his first generation of X-Men. The Juggernaut's rampage demolishes the school, and in "X-Men" (vol. 1) #13 it takes the combined might of the original X-Men and the Human Torch of the Fantastic Four to bring him down and remove his telepathy-blocking helmet. For all of Juggernaut's unstoppable physical might, he is vulnerable to his stepbrother's psychic powers — the ultimate example of mind over matter.

But nothing can truly stop the Juggernaut, and he becomes one of the team's most persistent foes. "X-Men" (vol. 1) #101-103 marks his first battle with the All-New, All-Different X-Men — Wolverine, Storm, Nightcrawler, and Colossus — alongside his partner, the mutant criminal Black Tom Cassidy (cousin of the X-Man Banshee: See what we mean about complicated X-Men family trees?). Fighting Professor X's stepbrother became something of a rite-of-passage for mutant teams like Excalibur, X-Force, and Generation X.

Despite their violent history, Professor X never gave up hope that his stepbrother Cain could turn away from his criminal life. His faith was seemingly rewarded in "Uncanny X-Men" (vol. 1) #412 when Juggernaut befriended a young mutant named Squidboy, who convinced him to join the X-Men. Though Cain initially resisted a brotherly relationship with Xavier, the two later had an emotional breakthrough while talking about surviving Kurt Marko's abuse as children. "X-Men" (vol. 2) #161 revealed that Juggernaut had been secretly working with Black Tom to infiltrate the X-Men, but his time on the team had genuinely changed him for the better.

Even as Juggernaut fought for redemption, however, he was tempted by the Gem of Cyttorak to abuse his tremendous power. He vacillated between the roles of hero and villain for years, until he finally rejected Cyttorak's power over him in the 2020 "Juggernaut" miniseries. Embracing a new path as a hero, Juggernaut joined Xavier and the X-Men on Krakoa. As a testament to the character's enduring popularity, Juggernaut won the X-Men Fan Vote to join the team in the "X-Men: Hellfire Gala 2023" special issue. As of "X-Men" (vol. 7) #1, Juggernaut fights in Cyclops's squad as one of the few non-mutant X-Men in the franchise's history. Whatever his future has in store, the Marko-Xavier family reunion is sure to be interesting.