This article contains spoilers for The Death of Doctor Strange: Avengers #1.
The unstoppable Juggernaut is a classic X-Men villain who derives his power from a demonic being called Cyttorak... but he isn't Cyttorak's most powerful weapon. A powerful mystical entity, Cyttorak was once worshiped on Earth - but he was banished from this plane of existence, stranded in a realm called the Crimson Cosmos. It was a similar fate shared by the Elder Gods such as Ch'thon, and like Ch'thon, Cyttorak left a channel of his power behind on Earth - the Crimson Gem of Cyttorak.
Anyone who handles the Crimson Gem of Cyttorak is transformed into a human Juggernaut, an avatar of Cyttorak's power whose sole purpose is to wreak havoc on Earth and ensure Cyttorak's name is not forgotten. The most well-known Juggernaut is, of course, Cain Marko; but there have been countless others over the centuries, all manifesting as forces of destruction so great they can only be matched by the likes of Thor Odinson or the Hulk. And yet, remarkably, it seems the unstoppable Juggernauts are not truly Cyttorak's greatest weapon.
The Death of Doctor Strange: Avengers #1, by Alex Paknadel and Ryan Bodenheim, reveals Cyttorak's greatest power is actually manifested through the Crimson Bands of Cyttorak. Sorcerers on Earth such as Doctor Strange have typically conjured the Crimson Bands of Cyttorak in order to restrain their foes, with all but the most powerful beings held captive by them. They actually made an appearance in Avengers: Infinity War, when Strange used them in an attempt to bind Thanos - and, of course, was unsuccessful.
This further explains why Cain Marko, the current Juggernaut, is more powerful than ever before. His connection to Cyttorak was disrupted, and he found his way to a mystic site called the Forge of Cyttorak, where he was given a new armor crafted from the power of the Crimson Bands of Cyttorak. This has given Marko a degree of freedom he never possessed before, because no longer is he an avatar of Cyttorak's destructive power; now he wields something far greater.
This naturally raises a curious question; why does Cyttorak allow sorcerers like Doctor Strange to draw upon his power? The most logical reason is that it ensures his name is not forgotten, for there seems to be a psychic connection between Cyttorak's power and his worship; to be forgotten would, therefore, weaken and perhaps even destroy him. And so Cyttorak prefers to lend a tool more powerful even than the Juggernaut to the Sorcerer Supreme.