Juggernaut Was Meant To Be Professor X, Not His Brother
Matthew Cannon 
Professor X's step-brother, Cain Marko, is better known as the unstoppable Juggernaut - but his dark god's first choice was actually Xavier himself!
The X-Men's Professor X was originally supposed to become the Juggernaut, not his step-brother Cain Marko. The mystical entity named Cyttorak was one of the Elder Gods who ruled Earth long before sentient life evolved on the planet, but he and his kin were banished to distant dimensions. He left behind him the fabled Gem of Cyttorak, and anyone who touches it is imbued with its power, becoming a human Juggernaut sworn to cause others to fear and honor Cyttorak's name.
One fateful day, a military deserter named Cain Marko stumbled upon the Temple of Cyttorak. Cain wasn't deserting from fear, but rather from anger, because his personality was unsuited to the army and he was seething with anger at being expected to follow orders. His hated step-brother Charles Xavier followed him, attempting to talk him round, but his every effort pushed Cain Marko further down the path that led to the Gem of Cyttorak. And so Cain Marko touched it, and he was transformed into the most famous Juggernaut of all.
But New Excalibur #15, by Frank Tieri and Jim Calafiore, reveals a secret Juggernaut has always known in his heart but tried to avoid admitting: Cain Marko wasn't the one Cyttorak intended to become his pawn. In this issue, Juggernaut - who's attempting to pursue redemption at last - is taunted by Cyttorak, and coaxed back to the path of violence. Seeking to hurt his avatar, to cause him to burn with anger once again, Cyttorak confesses Professor X was the one he'd really wanted. "After all," Cyttorak observes, "wasn't he the most powerful telepath on Earth? Wouldn't he have been a better choice than a lifelong failure with father issues?" But when the two step-brothers arrived at his temple, Cyttorak sensed Professor X lacked the anger he desired; anger that Cain Marko possessed in plentiful supply. And so he changed his mind.
This disturbing truth explains the lifelong feud between Professor X and Juggernaut. Cain Marko always sensed he was second choice, and hated Professor X for that fact. For his part, Professor X doesn't just fear his step-brother's powers - he also fears the image of himself he sees in Cain as the Juggernaut he could have become had things turned out even slightly differently. This is why, when Professor X went insane and spawned the monstrous entity called Onslaught from all his darkest thoughts, that being confronted Juggernaut first of all; because it knew Juggernaut's master had designs on the same power it now wielded.
Things have changed now. Juggernaut has broken Cyttorak's hold on his heart and mind, allowing him to choose his own course in life for the first time. He's become an ally to the X-Men, and even Professor X has accepted his presence on the living island of Krakoa. Ironically, though it took a long time, the Earth is better off that Cyttorak ultimately chose to empower Cain Marko as the Juggernaut, gifting that immense power to someone who would eventually join the side of the angels, rather than handing Professor X a legacy he was never suitable to adopt.
