As a child, X-Men founder, Charles Xavier, was tormented by his step-brother, Cain Marko. As intimidating as Marko seemed, he was nothing more than a bully. But when he was exposed to the Crimson Gem of Cyttorak, he was transformed into a human juggernaut.
Standing 9ft 5, weighing 1,900lbs, and commanding a strength that rivals the Hulk, Juggernaut is one of the X-Men's most daunting foes.
However, Juggernaut is at his most terrifying when he is running. If he builds up enough momentum, almost no force in the universe can stop him. Since he cannot get tired, he can run for as long as he wants.
On top of that, he is physically invincible and so, doesn't require air, heat, food, sleep, or water to sustain himself. He has a healing factor that allows him to withstand any attack, including one time when he was shredded down to his skeleton. Juggernaut is immune to draining powers so heroes like Rogue cannot defeat him by sapping his energy.
The easiest way to defeat Juggers is to knock him out with a psychic blast. But since his head is protected with an enchanted helmet, it is easier said than done.