First appearance: X-Men (1st series) #33
Description
The Crimson Cosmos is a world that exists, in some sense, within the Gem of Cyttorak. It was created by Cyttorak in part to house the prototype gemstone and, in the past, has served as a prison of timeless silence for the Juggernaut himself. Governed by arcane and ominous forces, this dimension contains a volcanic landscape with sulfurous steam wafting into the air.
While the Gem transforms its possessor into Cyttorak’s “Exemplar,” called the Juggernaut, in exchange the Juggernaut has an effect on the landscape of the Crimson Cosmos. The ground of the Cosmos is psychosensitive, so it forms into whatever the Juggernaut’s psyche subconsciously wills it to. In the Cosmos, there exist many chambers. In one such chamber, called the Hall of Cyttorak the Destroyer, the Cosmos’ master Cyttorak sits on his throne. Dr. Strange has a theory about the roads in the Crimson Cosmos, believing that all the roads eventually lead to Cyttorak’s throne. The Crimson Cosmos is the prison of Cyttorak and his essence is trapped there in.
Crimson Cosmos related plots
There have been few people who have visited the land of the Crimson Cosmos but, those who have, understand the curse that Cain Marko lives with. Centuries ago, heretic monks called upon the power of the demon Cyttorak. By accident, these monks botched their incantation and were only able to call forth part of Cyttorak’s essence. Unfortunately for them, this part was that of his most destructive aspect, which destroyed the heretic monks and scores of villages along its path. Thankfully, two novice magicians joined forces and banished this aspect of Cyttorak into the mystical ruby gem. While transcending into the gem, the elemental Cyttorak cursed the ruby, saying that whosoever came in contact with the gem would become a human Juggernaut. Inside the gem, Cyttorak created a dimension for himself. Knowing that he would spend a lifetime of loneliness, he began creating the landscape to his new imprisonment. [X-Men Unlimited (1st series) #12]
Sometime later, the Ancient one battled and defeated Xorak, who guarded the temple of Cyttorak on Earth. Finishing off the battle, the Ancient One sent the guardian into the gem to be with its master. It was many decades later before a being would come in contact with the ruby again. An oddity that can be pondered is, since time never passes in the Cosmos, how long must it feel to the inhabitants of the Cosmos before another being visits them? [X-Men (1st series) #33]
Several years after the curse transformed Cain Marko into the unstoppable Juggernaut, an experiment of Professor Xavier’s to undo this change went wrong and left him comatose. With the aid of Dr. Strange, two members of the X-Men were sent into the Crimson Cosmos to find the prototype gem. To their surprise, they were met by Xorak, who was not willing to fail his master a second time. The two mutants were almost beaten by the magical opponent, when suddenly they found Xorak’s weak spot – the Crimson Cosmos’ status as a world without time. When Marvel Girl threw her watch at him, Xorak suddenly raged rapidly and crumbled to dust. Back on Earth, the X-Men used the prototype gem first on Xavier to remove whatever influence had befallen him during the failed experiment, and then on the Juggernaut. When the prototype ruby made physical contact, the Juggernaut was pulled into the Crimson Cosmos, where he was trapped for an uncertain amount of time. [X-Men (1st series) #32-33]
Xavier, however, refused to sentence his stepbrother to such fate and built a machine that would slowly pull him back to Earth. When Cain eventually gained his freedom and returned to Earth, he was unaware that it was Xavier he had to thank his freedom for and wanted to wreak havoc on his stepbrother. However, Cain soon learned that his step-brother was now dead. In truth though, Xavier was only believed to have recently died, as it was actually the shapeshifter Changeling who had been killed in his place. Still, the Juggernaut’s stay on Earth was only short lived, as the gem sucked Cain back inside to live once more in the Crimson Cosmos. [X-Men (1st series) #46]
A short while later, Dr. Strange travelled to the Crimson Cosmos and lead the Juggernaut into Nightmare’s dream realm. Juggernaut showed a new trick that he learned while trapped in the Crimson Cosmos. Using mystic spells conjured from his hands, the Juggernaut caused Nightmare to shrink down to Juggernaut’s size and the two did battle. The culmination of their fight mistakenly released the imprisoned Eternity, who then banished the Juggernaut to another realm. The Juggernaut later escaped from that realm back to Earth, though not before losing again his newfound magical powers. [Dr. Strange (1st series) #128, Incredible Hulk (2nd series) #172]
After the departure of the Juggernaut from the Crimson Cosmos, Cyttorak became bored. He set out to create ecstatic elves to dance and sing praises to him, but this was not enough. 
When Galactus’ ship passed close to his dimension, Cyttorak sent his Ruby Bands after two of the ship’s occupants, Dr. Strange and Galactus’ herald, Nova. Trapped in the Crimson Cosmos, the two friends were separated, with Strange being imprisoned away from Cyttorak. The magician had only one resource left and that was to send forth a teleportation light to someone in the real world that had ties to the Cosmos. That person was the Juggernaut and, as the light captured Cain and pulled him once more into the Cosmos, he was enraged at being back in his former prison.
Eventually, the Juggernaut agreed with Strange that their only way out was to find Cyttorak and request their release. However, the deity had plans for Nova and Strange to serve as his priestess and priest. After meeting with Cyttorak, Strange convinced Cyttorak that he should let them go. Cain had other plans in mind and, upon seeing the Ruby Gem atop Cyttorak’s brow, he attacked the being that gave him his powers and wrested the jewel from him. However, Nova blasted the stone from his hands and it returned to Cyttorak, while Dr. Strange engulfed the Juggernaut in magical bonds. Having had enough of them, Cyttorak sent them all away to where they came from. [Dr. Strange (3rd series) #44]
Years later, the Crimson Cosmos was visited once again by Cyttorak’s Exemplar, the Juggernaut. The power of Onslaught was so intense that the entity had been able to rip the now bonded gem from Cain Marko’s chest and send the behemoth through it into the Crimson Cosmos. The unattended gem was sensed by both Dr. Strange and Gomurr, but the latter opted to venture into the Crimson Cosmos alone to bring Cain back. 
Once inside the gem, Gomurr faced off against Spite, a demoness who had apparently been sent by her brother, D’Spayre, into the Cosmos centuries before. Spite fought Gomurr over the Juggernaut and finally won, imprisoning Gomurr in magical shackles while she continued to manipulate Cain Marko to her liking. She brought him to Cyttorak for him to become the Earthen vessel of the deity, which is when the Juggernaut realized that he was tricked. Thanks to the timely arrival of Tar, Gomurr was freed and the two rivals put aside their disagreements to help the Juggernaut by magically empowering him to a degree that allowed him defeat Cyttorak and send them from the realm. Her master being defeated also allowed Spite to escape from the Crimson Cosmos. [X-Men Unlimited (1st series) #12]
It would be a while before anyone would venture into the Crimson Cosmos again. Cyttorak would sometimes use his influence and reach out from within it but it wasn’t until Cain was possessed by an entity called Kuurth, the Breaker of Stone, that anyone had reason to step foot there again. An Asgardian god known as the Serpent had sent down seven enchanted hammers to Earth. Cain picked one up and was taken over by Kuurth and transformed into an even more powerful being. His first action was to head for San Francisco, the home of the X-Men. As he created a path of destruction along the way, the X-Men sought to hinder his advance and attacked Cain in a variety of ways. 
When none even slowed him down, Cyclops decided to try a different approach and sent Magik, Colossus and Shadowcat into the Crimson Cosmos to talk to Cyttorak. There they told him of his avatar’s possession by another god and Cyttorak was so angry he took back all the power he gave to Cain. With the job done, the X-Men were about to leave but Magik stepped forward and offered herself to Cyttorak. He accepted her offer to become his new avatar but, before he could grant her the power, Colossus intervened. He couldn’t bear to see his sister become corrupted again, as she had only just reclaimed her soul. In her stead, Colossus offered himself to Cyttorak in her place and became the new Juggernaut. [Uncanny X-Men (1st series) #542-543]
Colossus struggled with both the power of the Juggernaut and the mental influence that came with it. When he soon thereafter also become a host to a fragment of the Phoenix Force, Colossus saw an opportunity to rid himself of Cyttorak’s power and travelled once again to the Crimson Cosmos with Magik. 
There, Colossus told Cyttorak about the Phoenix Force in the hope that he would take back his power like he had done with Cain. Cyttorak, however, saw the situation differently. He had similar goals to the Phoenix Force and he reveled in how much destruction Colossus was able to do now that he was even more powerful. When Colossus protested, Cyttorak became angry and told him that his word was law and that he would have to go on being his avatar, whether he liked it or not. With that, he expelled the two from his realm. [Uncanny X-Men (2nd series) #15]
Magik later revealed she had manipulated Colossus into taking on Cyttorak’s power in a bid to help him understand her more. She then took him to Limbo and reminded him of Cyttorak’s words the last time they met; “A Hell Lord is master of their own domain.” As the ruler of Limbo, her power superseded Cyttorak’s and she banished the demonic power from Colossus, leaving Cyttorak without an avatar once more. [Uncanny X-Men (2nd series) #20]
Whilst Cain would become empowered for a short time with the Gem of Cyttorak from an alternate reality, it would be a while before anyone heard from Cyttorak again. However, soon enough the demon grew tired of not being worshipped as a god and he manifested the gem back on Earth in the Korean temple in which it had resided for many years. A call went out to all those worthy of wielding the power of Cyttorak, including Colossus and Cain. Everyone descended on the temple but it was the Living Monolith who claimed the gem and became the new Juggernaut. The X-Men decided to visit Cyttorak himself to solve the problem and so Pixie teleported Cain, Rachel Grey and Colossus to the Crimson Cosmos.
As the demon lord sat on his throne, they questioned his choice of avatar and his very reason for wanting humans to worship him. They made him see that humanity would never worship him as a god, no matter how much destruction he rained down on them, and the only way he would ever be happy was to be killed by something that was truly unstoppable. Colossus offered himself up to be empowered once more on the condition that he would fight and kill Cyttorak. The demon accepted but decided to alter the terms of the offer by empowering Cain instead. He stripped the Living Monolith of his gifts and gave his new Juggernaut more power than ever before. Cain decided not to kill Cyttorak and instead took his rage back to Earth, where he set his sights on killing Cyclops. The X-Men intervened and defeated Cain but it can only be a matter of time before the Juggernaut crashes into the X-Men’s lives once more. [Amazing X-Men (2nd series) #15-19]
Involved Characters
Tar
Tar was one-half of the team of magicians that banished the dark essence of Cyttorak into the Gem of Cyttorak. In later years he became the Proctor of the Crimson Dawn. While often being rivals with Gomurr, he passed on his mantle to him after he died.
First appearance: Uncanny X-Men (1st series) #329
All Crimson Cosmos related appearances: X-Men Unlimited (1st series) #12
Powers: Can summon symbolic neon scorpions as Proctor of the Crimson Dawn, which act as his spies, couriers, and assassins, and can focus his power to infuse other people with beneficial or malevolent magicks
Gomurr
Gomurr and Tar first banished Cyttorak’s destructive essence into the gem. For many years Gomurr hid himself in part of New York’s China Town, but eventually he inherited Tar’s position as Protector of the Crimson Dawn.
First appearance: Uncanny X-Men (1st series) #329
All Crimson Cosmos related appearances: X-Men Unlimited (1st series) #12
Powers: Wield certain elemental and magical forces, allowing him to sense changes in the supernatural world, pass between dimensional barriers, summon up aetheric flame, fire blasts of pure energy, reach into the minds of others, shield himself and others from harm and detection, become intangible, and forge ninja servants out of ethereal mist
Xorak
This being was created by Cyttorak to be the guardian of his temple. During his travels the Ancient One opposed Xorak, and casts him into the gem to be with his master.
First appearance: X-Men (1st series) #33
Last appearance: X-Men (1st series) #33
All appearances: X-Men (1st series) #33
Powers: Scaled demon created by Cyttorak with limited magical power, enabling him to perform a variety of feats such as generation of energy bolts and force shields, illumination and illusion casting, out of sync with the regular flow of time
Juggernaut (Cain Marko)
Cain Marko’s life was forever changed when he came in contact with the Gem of Cyttorak. Several times in his life he found himself trapped in the Crimson Cosmos, where he had to oppose Cyttorak himself, though was also provided with the chance to better learn how to better use the gem.
First appearance: X-Men (1st series) #12
First Crimson Cosmos related appearance: X-Men (1st series) #33
All Crimson Cosmos related appearances: X-Men (1st series) #33, 46, Dr. Strange (1st series) #128, Dr. Strange (3rd series) #44, X-Men Unlimited (1st series) #12, Amazing X-Men (2nd series) #18
Powers: Infused with the power of the Ruby Gem of Cyttorak that gives him immeasurable strength and endurance, a massive indestructible body reinforced by an inertia-cancelling force field, and an enchantment that renders him virtually unstoppable once in motion
Dr. Strange (Dr. Stephen Strange)
Some of Dr. Strange’s spells draw their power from Cyttorak, and apparently his mystic abilities also make him very sensitive to what happens in the Crimson Cosmos. Several times he has aided other to get in or out of there, and once he found himself trapped in the place himself and had to summon the Juggernaut to bail him out.
First appearance: Strange Tales (1st series) #110
First Crimson Cosmos related appearance: X-Men (1st series) #33
All Crimson Cosmos related appearances: X-Men (1st series) #33, Dr. Strange (1st series) #128, Dr. Strange (3rd series) #44, X-Men Unlimited (1st series) #12
Powers: Sorcerer Supreme of Earth able to tap magical power through his own psychic potential and the ambient mystical energy of the universe, enabling him to perform a variety of feats such as telepathy, psychokinesis, mesmerism, illusion-casting, astral projection, generation of energy bolts and force shields, summoning of distant objects, illumination, teleportation through time, space, and dimensions, and the animation or transmogrification of unliving matter, able to utilize magic found within extra-dimensional entities, allowing access to power such as the Flames of Faltine, the Seraphim Shield, or the Crimson Bands of Cyttorak, wears a coat or cloak of levitation that enables him to move through the air under mystical direction, and the Eye of Agamotto that allows him to see through lies or illusions to perceive the truth inherent to any person or object
Nova II (Frankie Raye)
Frankie Raye was about to join the Fantastic Four when Galactus arrived on Earth. In order to save the planet, Frankie offered herself to become his new herald, and was instantly transformed into Nova.
First appearance: Fantastic Four (1st series) #164
Last appearance: Silver Surfer (3rd series) #75
All Crimson Cosmos related appearances: Dr. Strange (3rd series) #44
Powers: Flammable chemicals altered her body to give her pyrotechnic powers which have been added to and amplified to near-infinite levels by the power of Galactus, giving her tremendous strength, endurance, and resistance to physical injury, the ability to enter hyperspace and fly at near-light speed in normal space, survive in the vacuum, and produce radiance across the electromagnetic spectrum as cosmic fire she can direct at will
Spite
She is the sister of D’Spayre who banished her to the Crimson Cosmos centuries in the past. Spite tried to form an alliance with Cyttorak himself, but actually it was more a master-slave relationship than equal partners.
First appearance: X-Men Unlimited (1st series) #12
All Crimson Cosmos related appearances: X-Men Unlimited (1st series) #12
Powers: Demoness specializing in the creation of illusions and falsehoods
Colossus (Piotr Nikolievitch Rasputin)
First appearance: Giant Sized X-Men #1
All Crimson Cosmos related appearances: Uncanny X-Men (1st series) #542-543, Uncanny X-Men (2nd series) #15, Amazing X-Men (2nd series) #18
Powers: Transmorph able to convert his entire body into organic steel with enormous strength and durability; as avatar of Cyttorak he possessed significantly increased strength, invulnerability, superhuman speed and tolerance for pain, mystical healing abilities, inertia-cancelling force field, regenerative armor, and an enchantment that rendered him virtually unstoppable once in motion
Magik (Illyana Nikolievna Rasputina)
First appearance: Giant Sized X-Men #1
All Crimson Cosmos related appearances: Uncanny X-Men (1st series) #542-543, Uncanny X-Men (2nd series) #15
Powers: Summon stepping disks that can teleport through time and space, powerful and moderately-trained sorceress, Soulsword can disrupt mystical spells and channel her own magical skills
Shadowcat (Katherine Pryde)
First appearance: X-Men (1st series) #129
All Crimson Cosmos related appearances: Uncanny X-Men (1st series) #542-543
Powers: Molecular repulsion allows her to enter an intangible state, letting her move through solid objects, walk on air, and disrupt electronic systems
Rachel Grey (Summers)
First appearance: X-Men (1st series) #141
All Crimson Cosmos related appearances: Amazing X-men (2nd series) #18
Powers: Telepath able to read minds, project thoughts, send out her astral form, and manipulate thoughts to control minds, cast illusions, and alter memories, psychokinetic able to lift, direct, and manipulate physical objects, project psionic force blasts, generate force fields, and fly, able to project the consciousnesses of herself and other humans through the fabric of time and space
Pixie III (Megan Gwynn)
First appearance: New X-Men: Academy X #5
All Crimson Cosmos related appearances: Amazing X-Men (2nd series) #18
Powers: Fairie-like mutation gives her the ability to excrete "pixie dust" that causes hallucinations in other people and rainbow-colored wings enabling her to fly, black magic replaces a portion of her soul, letting her summon a souldagger, teleport herself and others, and manipulate rudementary magicks