Cain Marko (Earth-21399)

Early Life
Cain Marko's biological mother abandoned the family shortly after his birth, causing his father to descend into depression and leaving Cain with severe attachment issues. Sometimes he would act out to try and get his father's attention, but this caused Kurt to grow increasingly disappointed with Cain.

When Cain was about twelve years old, Kurt remarried to a wealthy socialite named Sharon Xavier after Brian Xavier, Sharon's previous husband and Kurt's coworker, died in a workplace accident. Kurt took an immediate liking to Sharon's son, Charles, for his scientific curiosity and gentle demeanor – almost as quickly as Cain began to hate Charles for being the object of Kurt's affection.

When Charles was sixteen, his telepathic powers went haywire and he found himself linking his mind with Cain's, experiencing his stepbrother's feelings of loneliness and pain. Cain, thinking that Charles had been using this gift to brainwash their father, resisted the link and took up a baseball bat, intent on killing Charles. Kurt intervened at the last minute, overhearing Sharon pleading with Cain, and was accidentally killed by his son. The traumatized Cain was swiftly arrested and imprisoned, swearing revenge on Charles as he was dragged away.

Mercenary Life
After his release from prison, Cain befriended an Irish mercenary named Thomas “Black Tom” Cassidy, and they eventually took a job aiding the communist revolutionaries during the civil war in Symkaria, operating out of an old Nazi base storing gold bars. It was here where Cain had his first meeting with Charles since they were separated, with Charles and his friend, Erik Lehnsherr, attempting a rescue mission for their mutual friend, Moira MacTaggert.

Erik had the mercs at his mercy and attempted to execute them, but Charles prevented this with his telepathic powers, noticing that Cain was among them. After Erik left, Charles and Moira took Cain into their own custody, with Charles promising to help his stepbrother heal their wounds back home. But as the three of them were leaving Black Tom's base, they came under fire from Symkarian military forces, forcing them to flee into a nearby cave system.

Becoming the Juggernaut
While wandering the caves, the three found a vast chamber adorned with ancient writings. During their investigation, Cain noticed a small red stone amid a pile of other rocks and instinctively grabbed it. As he did this, the stone erupted in a flash of red light and transformed Cain into a raging beast who attacked Charles and Moira, collapsing the cave system around them in the process. Charles and Moira managed to escape, although the falling rubble crushed Charles' legs, leaving him unable to walk again. Cain was buried in the cave and presumed dead, but had in fact survived.

Enraged, Cain convinced himself that Charles had left him to die in the cave, luring him inside with honeyed words. Now more determined than ever to kill his brother, Cain singlemindedly started digging his way out over the next several years, his hatred and anger becoming all-consuming. As his mental state deteriorated, a voice started to whisper inside Cain's mind, eventually forming a single coherent statement as Cain finally dug himself free:"He who has touched this gemstone and lived is now bound by the Crimson Bands of Cytorrak. Henceforth, he who bears this burden receives the blessing of the Rage Father, and shall be forevermore a human juggernaut."