Juggernaut (Cain Marko) is a fictional character appearing in American comic books published by Marvel Comics. Created by writer Stan Lee and artist/co-writer Jack Kirby, he first appeared in X-Men #12 (July 1965) as an adversary of the eponymous superhero team. Since then, he has come into conflict with other heroes, primarily Spider-Man and the Hulk.
Cain Marko is a regular human who was empowered by a gem belonging to the deity Cyttorak, becoming a literal human juggernaut. He possesses superhuman strength and durability, and is virtually immune to most physical attacks; his helmet also protects him from mental attacks. Although not a mutant, Juggernaut has been featured as a prominent member of the Brotherhood of Mutants. He is also the stepbrother of Professor X.
Source: Wikipedia, "[en.wikipedia.org/wiki/Juggernaut_%28comics%29 Juggernaut (comics)]", available under the CC-BY-SA License.