Cyttorak is one of principalities - magical entities of vast mystical powers. His origin is shrouded in mystery. Once he was worshiped on Earth, and by unknown circumstances was banished to outer-dimension known as Crimson Cosmos.
Cyttorak is stated (by marvel) to be old anywhere from several millenia to several billions of years old. He appears in one of his 2 known aspects.
First aspect is a God-looking one which is a source of power to sorcerers and powerful mystical entities like Dormammu, Umar, Zom ...
Second aspect is a Demon - looking one that empowers Juggernaut and which is titled as "His most destructive aspect". This title strongly refers that there are also other aspects of Cyttorak. And what's even more interesting, his most destructive was set free by monks who tried to summon Cyttorak to Earth again and this aspect was later imprisoned in the Crimson Ruby. So there is strong indication that aspects are sentient on there own. During Infinity War, Cyttorak commented that he actually prefers to be in a God-looking aspect. It was shown that after destructive aspect was imprisoned in the Ruby, Cyttorak himself transported the Ruby outside of the temple on occasions in order to find human avatars easier.
Cyttorak's Crimson Cosmos was shown to be one of many pocket dimensions in the Marvel Mystic Arcana and has been traveled to by users with competent magical ability.
Cyttorak participated in the Octessence, a wager between eight vastly powerful inter-dimensional beings who decided to find out which was the most powerful by giving a fraction of their power to eight human avatars that would fight in their honor. Each of them placed an item in their temples for someone to find, after the first item was found people would be magically drawn to the remaining seven. The collapse of his temple is assumed to be the reason why the other Exemplars did not emerge after Cain Marko became the Juggernaut.
Cyttorak was one of the many beings who tried to recruit Dr. Strange.
Cyttorak (most destructive aspect) was later seen in New Excalibur, and most recently in Captain Britain & MI-13 #3 where he was released from a magical prison.
Upon finding out that Juggernaut has forsaken him for Kuurth, Cyttorak takes his power back from Juggernaut and gives it to Colossus.
Losing His Avatar
After each inheriting a portion of the Phoenix Force, Colossus and his sister Magik confront the destruction lord in the Crimson Cosmos, asking him to free Colossus of his burden. Cyttorak refuses on the grounds that Colossus' reign of destruction was like a perpetual feast to him and that he made for a far better avatar of destruction then his predecessor, Cain Marko. When the siblings threatened them with their new power, Cyttorak warns them that even 1/5 of the Phoenix Force was insufficient to even challenge him.
Later Illyana transports her brother in Limbo and, being the demon lord of that dimension, severs the bonds that enslave Colossus, freeing him Cyttorak's taint. It is unknown how Cyttorak will react to the loss of his latest, favorite avatar.
Powers and Abilities
Cyttorak is a powerful magical deity, being most powerful within his Crimson Cosmos. Powerful magic users such as Doctor Strange, The Ancient One, Dormammu and Zom have invoked Cyttorak's power. The Vishanti have shown at one point to be wary of angering Cyttorak and advised Doctor Strange not to intervene with Cyttorak or any of his creations - although they did enter Cyttorak's realm and demand him to release Doctor Strange from his possession.
The fraction of his power given to the Juggernaut was stated by D'Spayre to be able to control the very fabric of the universe itself, though this is looked at as hyperbole from D'Spayre as he is a mere Fear Lord that is insignificant to any godlike entity. However, it does show that Cyttorak is more powerful than the Fear Lords.
Cyttorak's magic has allowed Juggernaut incredible durability, even keeping him alive after being stripped to bare bones. The Realm of Oblivion was originally shown to be unable to kill Juggernaut by aging him, though this was retconned to where Oblivion's realm actually did kill Juggernaut and only after being thrown out of the realm was Cyttorak's magic able to restore his avatar back to life.
When his avatar Juggernaut learned some spells from Crimson Cosmos he was able to overpower demon Nightmare in his domain. At that time Nightmare imprisoned Eternity through a plot device as used every sleeping sentient being in the universe to cause Eternity to fall asleep, which allowed Nightmare to control him without Eternity able to fight back. Some would mistakenly believe that Cyttorak's power would be on par with the most powerful cosmic entities because Nightmare beat Eternity through plot device and Nightmare was defeated by Juggernaut. However, Cyttorak has been punched out in his own realm by Juggernaut and Nightmare has been put in a choke-hold so Cyttorak is not even close to the cosmic abstracts in power.
Cyttorak's energies grant his avatar virtually limitless strength and durability
Cyttorak has demonstrated that he can create life from nothing, as he created an entire race of elves just to worship him in the Crimson Cosmos, and he also created magical servants in order to protect his temple in South Korea. Those who were invoking Cyttorak for power were granted a variety of spells, and each had a certain effect. Those spells are: Crimson Bands of Cyttorak, Scarlet Sphere of Cyttorak, Crimson Shields of Cyttorak, Crimson Crystals of Cyttorak, Cage of Cyttorak and others.
Cyttorak once used his tendrils to capture the cosmic spaceship with Galactus, Silver Surfer, Nova and Doctor Strange on it and they were helpless against him. The tendrils teared through dimensions and sucked the spaceship into the Cyttorak's realm.
Recently Cyttorak overpowered 1/5 of the Phoenix Force which was in Colossus without any effort. This feat is not all that impressive though because the Phoenix Force has been driven away by a few members of X-Men and Ultra Force, and also that Cyttorak is quite omnipotent only in his realm.
During the Trion Saga his avatar was powered up to the level on which he was able to cause a crack in a dimensional barrier by punching it, without the Earth being in any danger whatsoever. And when Cyttorak's energies (which were used for additional power up) got released from Juggernaut they started destroying the small pocket realm of the Trion gods. The rampage of Juggernaut during the Trion saga left many dimensions merged together.