WARNING: The following article contains major spoilers for Deadpool 2, in theaters now.
Find the biggest guy in prison and make him your-- no, as young mutant Russell discovers in Deadpool 2, that's not exactly practical advice. Ryan Reynolds' Wade Wilson tells him to make powerful friends instead and Russell (Julian Dennison) does just that: When Deadepool temporarily abandons the kid after his first fight with Cable, Russell sneaks into the maximum-security sector of the Ice Box mutant prison, and befriends an unseen behemoth, whom we later learn is none other than longtime X-Men foe the unstoppable Juggernaut.
While we've seen hints in the sequel's promos of Juggernauts reintroduction, fans were uncertain for a long time. The last time we saw Cain Marko in live-action was in 2006's X-Men: The Last Stand, played by Vinnie Jones in an oddly revealing costume that included what can only be described as a metal phallus on his head. Unsurprisingly, the film's depiction drew a lot of criticism, especially from fans of the comic book character.
For those who aren't familiar with Juggernaut, he's not a mutant, but the human stepbrother of X-Men founder Charles Xavier. Cain's father, Dr. Marko, favored Charles, which caused Cain to bully his stepbrother. That in turn drove Dr. Marko to beat Cain. Years of jealousy and abuse, coupled with the nature of Xavier's powers, caused Cain to view Charles as his enemy. Upon hearing about Charles' mutant ability from his dying father, Cain developed the delusion that Charles had always been invading his thoughts. Eventually, it all became too much for young Cain to handle, so he ran away and became a mercenary before joining the U.S Army. It was during that time that Marko stumbled into the Temple of Cyttorak and found the mystical gem that turned him into the unstoppable avatar of Cyttorak.
X-Men: The Last Stand presented audiences with a character who bore the right name and was more or less unstoppable, but didn't quite seem like the Juggernaut fans knew. Unlike his comic book counterpart, the film's Juggernaut was clearly stated to be a mutant without an ounce of mystical aid from otherworldly crimson deities. While comic book Juggernaut is only invulnerable duet to a mystical force field, the film's Juggernaut seemed to lack that limitation. You might also notice the film's Juggernaut was pretty much the same size as a human instead of a gargantuan mass of muscle and mystic powers. All things considered, that's actually one of the forgivable flaws of the adaptation.
What wasn't forgivable, however, was transforming a relatively complex character into a borderline generic villain by stripping him of any depth and connection to the X-Men through his relationship with Xavier. It's the one thing that elevated Juggernaut above all the rest of the antagonists in terms of motivation: He didn't want to take over the world, and he didn't really set out to hurt people, just those who got in his way or threatened his friends and allies.