At the beginning of time Urizen was one of the missing threads in the universe who ruled along with the other Elder Gods who together brought balance to the universe. Urizen was one of these Elder Gods, a great deity that existed before even Heaven and Hell. His sole duty was to consume souls, freeing them from the wheel of life and death and perpetuating conflict as a means of cleansing the universe. The easiest way to maintain peace is to destroy those who created conflict or to have them destroy themselves. Urizen represents balance in that he ends existence. This frustrated the upstart factions of both Heaven and Hell and kept both sides in weakened conditions. They're armies needed souls in order to increase their ranks. Urizen was a direct threat to this need. As long as he was free to roam the universe neither side could gain an upper hand over the other. Thus they teamed together for the first time and defeated Urizen banishing him from this level of reality, the only thing that they could do to him since he was truly an immortal.
The Cult of Urizen
A cult that devoted itself to Urizen and attempted to harness his power and bring about his return. They felt that there was a lack of a balancing force between Heaven and Hell and that in the absence of this force Urizen would rise to fill that void. It all began with a series of ceremonies which began with 13 souls and during each full moon one member of the group was chosen as the sacrifice. The sacrifice would be hunted down by the group, killed, and then eaten in a cannibalistic ritual. The act of consuming the sacrifice was supposed to fuse their souls together and the goal was to continue until only one soul remained, which would be the vessel through which Urizen would someday return. However, the ceremony was interrupted when Spawn found out and altered the current sacrifice with his magic. When they consumed their friend the remaining members of the cult began to vomit up their own organs, insects and bile which lead to the death of the remaining, ending the threat. Or so it seemed.
The release of Urizen
Unknown to Spawn, someone else had a plan for Urizen. Two minor Gate-opener demons, Ab and Zab, were sent to earth and possessed the bodies of two murderers who died in a car crash that Spawn had caused outside the town of Malice, Pennsylvania. They went to a nearby diner and waited until they had 13 innocents to sacrifice. They executed them and then took them to a nearby hill where they painted a mystical emblem on the ground and burned the bodies, completing an opening spell that released Urizen from his banishment and allowed him to return through the smoke. As they worked they referenced that Urizen had been forgotten over time. Only a few really knew of his existence, and only limited information. William Blake was one such person and he wrote about him in The Book of Urizen, but like the cult most of what Blake believed was wrong.
Spawn sensed that a great power had arisen and headed to face Urizen, but was easily defeated. Urizen had nailed Spawn to the Earth with a sign and Spawn was then pulled into Greenworld where he was given a gift of great power with which he could defeat Urizen with when he returned to Earth. Angela was there when Spawn awoke, eager to aid him in his fight. She had captured the demons Ab and Zab and had found out what they were up to. Meanwhile, Urizen was laying waste to the land and the forces of Heaven were about to go to Earth to stop him. This would have jump started the Apocalypse, because it would have also permitted Hell to invade earth. Angela went to stop the Angels while Spawn fought Urizen. Angela returned, and Spawn used his new powers to create a wall of trees to slow Urizen down.Urizen was defeated With the Chains of Hell, the Ribbons of Heaven and the Gift of The Greenworld (a powerful necroplasmic blast charged with the four forces of nature) and the Earth opened up to swallow and imprison him. Interrogation of Ab and Zab led Spawn and Angela to find that Malebolgia had been the one who had sent them on their mission in the hopes that he would draw Heaven into the war early, since his army was far larger and more powerful. This led to the confrontation between Spawn, Angela and Malebolgia that would lead to Angela's and Malebogia's death. Leaving Spawn to rule The Eighth Sphere of Hell.
Possessed by the Black God
After Spawn and Angela had used their combined powers to encase Urizen within the Earth he was thought to be defeated. However his hand was encased in stone and stuck out from the spot where he was swallowed and was deemed a natural landmark called The Demon’s Right Hand. Preston Miller and his two brothers were playing at The Hand one day when Preston stepped on something sharp. It appeared to be a small black rock that bore into his foot, but really it was a piece of the god himself. The Miller Boys were possessed by the spirit of Urizen, through the minute piece that lived inside Preston. He was filled with all of the Dark God’s knowledge, especially the events that occurred in Malice. Urizen amplified their cruelty and caused them to taunt and harass a boy at school they called “Piggy.” They captured him, tied him up in a barn and were ready to slit his throat when Spawn arrived. Preston began to transform into a pig-like beast and screamed,
"I am The Void. I am The Night. I am The Wolf that hunts the child in the crib. I am The Darkness that knows no dawn. You are the door. You are the gate through which my thunders shall pass. I am the cold breath of The Grave. I am The Eater of Worlds. I am The Destroyer. I shall bury you."
Realizing what had possessed Preston he then used his powers to tear the shard of Urizen out of Preston’s chest and presumably obliterated it. Whether he destroyed it or teleported it back to Urizen’s prison is unknown.
Urizen has many powers due to his being a supreme deity. His size increases as he consumes souls which are negated as they become part of him and he has an ability to spread malice in the souls of man and release them of their inhibitions so that they might commit horrific deeds. He also has the abilities to disappear into a cloud of smoke and appears in a similar form upon his release. He has the ability to possess beings of whom he comes in contact with. The Greenworld fears his very presence on The Earth because his very existence in this realm poisons the planet itself. Since he is a God he is immortal and cannot be killed. The only way to stop him is to imprison him with powers from Heaven, Hell and Earth.