Zadkiel has spent a millennium doing Heaven's dirty work, fighting hell's incursions onto Earth and pruning the worst of the worst from the human population. Over the years, he's come to despise all of humanity, not just the sinners. Now he figures he can do a better job of sitting on the throne of heaven than God. And if he succeeds in his war against heaven, the first order of business will be wiping out the wretched human race.
Zadkiel has come into conflict with God. He believed that he needed the power of the Spirits of Vengeance to help him win his war against Heaven and Hell. Zadkiel revealed to John Blaze that he was not a demon of vengeance as he had come to believe due to his being a spirit of vengeance, when actually he is being used as an angel of vengeance. In actuality Roxanne, his ex-wife, made a deal with Mephisto, in hopes that she could save Johnny from life time of damnation in Hell. However, Zadkiel was easy to persuade he had already declared his own war on heaven. He is attempting to overthrow God himself, and he saw Johnny, or the Ghost Rider, as the ideal pawn to complete his intentions.
Zadkiel ultimately won his war when his willing pawn, Daniel Ketch, blindly led the Black Host into war with Blaze and the last remaining Ghost Riders. Ketch took the powers of Blaze and his allies, Molek, Bai Gu Jing, Baron Skullfire, and Marinette Bwa Chech. Upon delivering these gifts to Zadkiel, Ketch was cast out of Heaven and had his eyes opened to his master's sinister plan. Daniel took as much Ghost Rider power with him as he could, but it wasn't enough to prevent Zadkiel from overthrowing the kingdom of God.
As his power grew, Zadkiel was confident he would become God, but Blaze and Ketch would not stop their pursuit of him. To make matters worse, a cult managed to manufacture the Antichrist which could bring about the apocalypse and remove Zadkiel from power. Sending Blackout, Deacon, Orb, Big Wheel, Madcap, Scarecrow, Vengeance and Trull to do his dirty work, Zadkiel thought his victory was imminent. However, a gateway to Heaven, guarded by the Gun Nuns, gave passage to the Ghost Riders, allowing them to stand face-to-face with Zadkiel - proving the Antichrist was the least of his concerns. He defeated them easily which only fueled his arrogance, but when they returned with an army of Ghost Riders, Zadkiel trembled. For all his power, only the one true God could destroy a Spirit of Vengeance, and Zadkiel painfully discovered he would never achieve that right. Zadkiel was sent to Hell where he would suffer eternal torment.