This was more than a simple sibling rivalry. The feelings Cain had against  his stepbrother were deep rooted. Cain was abused harshly by his father for his failures in school and life while his stepbrother Xavier found success in all that he did. But   unknown to Cain then,Charles Xavier was a mutant with the ability to read others' minds. This was an ability he had no aversion to using for his own purposes. Not only did Charles excel academically because of this but by using his telepathy Charles became a star athlete as well. He knew what his opponent's move was going to be before he made it and over the years amassed several trophies for his prowess. Charles' success at every endeavor consumed Cain with jealousy and he would torment his stepbrother at any opportunity. But when the time came that Cain sought to fight Charles,Xavier  used his mental power to deliver Cain a swift defeat. As his control over his power grew Xavier would begin entering Cain's mind. Cain's memories and most private thoughts were read by Xavier. Cain's jealousy and feelings of inadequacy toward his stepbrother were no longer his dark little secret. Xavier now  knew of it all. This only helped ensure that Cain would hate Charles Xavier in the truest sense of the word.
One day in an argument with his father in his lab,Cain knocked over a group of  volatile chemicals. This started a deadly blaze which consumed the laboratory. Kurt Marko managed to save Cain and Charles but at the expense of his own life. Before dying Kurt revealed that he probably could have saved Brian Xavier those years ago,but he didn't try. He also left Charles with a warning to beware of Cain should he ever find out about his psychic power.
 
     Eventually Cain and Charles would grow up and go on their separate 
paths. Charles would go off to see the world,Cain would become a mercenary. 
This occupation  would land him in a third world prison where he met fellow 
mercenary Tom Cassidy. The two became fast friends. During the Korean War  as fate would have it,Charles Xavier was assigned to his same unit. One day their battalion was under fire against hopeless odds. To avoid near certain death or worse Cain fled from the battle toward a hidden cave. Charles followed to convince him not to abandon  his unit but it was to no avail. Inside they stumbled upon a large,ancient gem with an inscription on it claiming that whoever read it while touching the gem would become a human juggernaut. Against Charles' suggestions Cain did so and no sooner had he finished reading the words than did the gem begin infusing energy into him. His body grew,rippling with power. The transferrence caused the the cave to begin to crumble. Charles,seeing Cain was beyond saving,fled before he himself was buried under the rubble.
 
     Charles would move on and return back to the US
where he began work on human/mutant relations presuming,and more importantly,hoping that his  stepbrother  had died in the cave-in. Cain afterall had just been buried under trillions of tons worth of mountain. Years later Xavier would learn of Cain's fate under the mountains.  The claim was not an empty promise. Cain and Charles had found the gem of Cyttorak. Cyttorak is an other-dimensional god with many Earth followers in Asia. Cain Marko had indeed become a human juggernaut. The gem had made him unstoppable and he had survived. He was now also one of the strongest beings on the planet who wanted 
Charles Xavier dead and set out to do it himself. He tracked down 
Xavier to New York where he had now formed a group of mutants known as the 
X-Men. They served as the first obstacle between Cain and his stepbrother. 
With his newfound power Cain(now called The Juggernaut) made short work of Xavier's 
team  with very little effort,but with aid from the Fantastic Four's Human Torch they did manage to set up a psychic attack 
from Xavier which was enough to defeat The Juggernaut.
The Juggernaut would again make an attempt on Xavier's
life and through the aid of Doctor Strange,he was sucked
into the dimension of Cyttorak  known as
the Crimson Cosmos.  But this would not be 
the last of him.
 
 
     Eventually Cain was pulled back to 
our dimension mistakenly through human machinations and would reunite with his
good friend Tom Cassidy and the two mercenaries would form a partnership with their
deep friendship as their bond. With Black Tom as the
mastermind and Cain as the muscle the duo embarked
on a successful career. With The Juggernaut's staggering
might no assignment was too big for them now,once even
holding two of the country's wealthiest people hostage
inside the World Trade Center. The Juggernaut
became one of the most wanted criminals on the planet.
Proving himself unstoppable by even the mightiest of heroes
and most powerful villains. He often was seen single-handedly
battling whole teams of superpowered individuals and was confronted by the likes of Hulk and even the thunder
god Thor. But still he  remained indomitable
against them. 
Even when somehow slowed down he always
emerged basically unscathed. His power was feared by anyone who knew of him. And with good reason.
     When The Juggernaut set out to accomplishish
something,there was little anyone  good or evil could do about it. With Cassidy leading and Cain providing the unmatched brawn
they were to  become
very wealthy criminals. And when not working with Tom The Juggernaut still found trouble even if it meant
having to look for it. He has had run-ins with the military both in the United States and abroad.
The nature of Cyttorak is a destructive one and as such The Juggernaut is prone to violent
rampages that can sometimes be orchestrated with little concern for human life.
The nature of Cyttorak amplifies Cain Marko's naturally malicious persona.
Though always a brutal bully and sociopath,it is speculated that the influence of Cyttorak's power is what 
gives Cain his  capacity to kill indescriminately.
      Little did anyone expect or imagine,The 
Juggernaut would later see a strange twist of fate. He for once would be the one terribly 
 brutalized in a battle. Onslaught,a bizarre amalgamation of Charles 
Xavier and Magneto,would belittle The Juggernaut,inexplicably defeating him and trappping him in the 
very gem 
of Cyttorak which gave him his power. Inside the gem Cain,aided by Gomuur The Ancient and 
Tar,destroyed the god Cyttorak and the gem as well,freeing Cain.
     Recently it has been discovered that Cain becoming The Juggernaut was 
no accident. He was destined to from the beginning to compete with 7 other 
avatars to prove which god was the most powerful. With the help of the 
Avengers this godly battle royal(which was supposed to devastate the planet) 
was averted. The Juggernaut defeated most of the avatars one by one and 
destroyed their machine which was supposed to eliminate man's free will.