As any major “X-Men” fan knows, Charles Xavier is actually the stepbrother of Cain Marko. The two became part of the same family unit when Cain’s father, Kurt Marko, married Charles’ mother, Sharon. Years later, the two step-siblings would deploy and serve together in the Korean War, which led to Cain discovering a cave dedicated to the mystical entity Cyttorak.
This is how the Juggernaut gains the muscle and massive size that have since become trademarks of the character. As for his hatred for his younger stepbrother, Charles, that is explained by the childhood that the two shared after their parents were married.
After the wedding, Cain’s father, Kurt, begins to favor Charles over his own son, regularly mistreating and even abusing Cain as a result. This causes Cain to begin bullying Charles and helps to explain the close connection and familiarity between the two foundational X-Men characters. Furthermore, it helps to demonstrate why Juggernaut understands Charles’ powers so well.
In more recent times, the X-Men villain has also acquired a telepathy-blocking skullcap, which he uses as a secondary shield in case his helmet is removed. Though Magneto’s headgear change for the movie was in response to a plot hole, it’s entirely possible, though it’s never been confirmed, that the idea sprang from the film’s writers being familiar with Juggernaut’s comic book history.
