Zankou is an antagonist that appears in the television show Charmed, serving as the main villain of Season 7. He was an ancient, ruthless, and extremely powerful upper-level demon who was feared, even by his own kind. Intelligent and cunning, his understanding of the human thought made him able to perceive, manipulate and prey on the weaknesses of his enemies.
His greatest feats include the Crusades, the September Massacres, and the Black Plague. His abilities and ambition became so great that he eventually contested the Source of All Evil for control over the Underworld. However, the Source was able to imprison Zankou within a magical barrier deep within the Underworld, unable to break free.
Zankou formed one of the biggest threats ever to the Charmed Ones but his reign of terror came to an end in 2005 with the destruction of the Nexus beneath the Halliwell Manor, which took him along with it.
Freed from imprisonment
Zankou was released from his prison by a group of demons who believed he was the only one who could prevent the impending attack of the Avatars. Although several demons were opposed to his release, it was eventually decided that he must be released because he was their only hope. Reluctantly, several demons went to his prison and freed him. Zankou then revealed he was aware of everything that had happened in the world and proceeded to absorb the powers of a Shapeshifter. He then used this power to get close the Seer Kyra, who was planning on betraying the demons, and vanquished her for her betrayal.
Fight against the Avatars
Originally, he helped the Charmed Ones in their fight with the Avatars along with Leo Wyatt and Kyle Brody, realizing that their Utopia threatened the very survival of demonic existence (as well as the free will of all others, which he used to gain allies).
Attempt to control the Nexus
Zankou wanted to control the Nexus, however, his attempts failed. The first time was in Scry Hard, when he tried to get the sisters to cast a spell so that he could get the Nexus, but his attempt failed because the Nexus could not choose between the Power of Three and Zankou. Instead, it went to Leo. The second attempt was in Something Wicca This Way Goes...?, when he took over the Halliwell Manor, while the Charmed Ones were at Magic School, and took in the Nexus. However, the Charmed Ones were spying and used a spell to draw it out of him.
Stealing the Book of Shadows
After the threat of the Avatars had passed, Zankou began to mobilize the Underworld in hopes to control it. He attempted to steal the Book of Shadows on various occasions. He even hired a demonic alchemist to brainwash resurrected zombie innocents that the Charmed Ones were previously unable to save into attacking them (two of which he had killed that same week, one by his own hand, just for the occasion).
Stealing Phoebe and Piper's powers
After breaking through the protective barrier that the Book of Shadows wields due to weakening the sister's bond as well as their confidence in themselves and in their magic, Zankou retrieved the Book and created the potion To Separate a Witch from Her Powers in a diabolical plan to steal the Charmed Ones' powers. He then attacked the sisters in the Attic and distracted the girls by firing an energy ball at Piper Halliwell, who Paige and Phoebe then tended to. With their backs turned towards Zankou, he threw the potion at Phoebe and absorbed her power of Premonition. After the acquisition of this power, he was able to foresee the sisters going to seek help from the Vampire Queen and he got to her first. The power also enhanced his prescience and sensing abilities.
The sisters went to the Queen for assistance and she feigned being on the girls' side. Thinking the Queen was on their side, they then orbed to the Manor where Zankou was waiting for them; he told them he got to the Queen first. He attacked and threw the potion at Piper and absorbed her powers of Molecular Immobilization and Combustion. Zankou then used the Combustion power on Piper sending her flying backwards. The only powers he wasn't able to absorb from the sisters were Paige's powers, because she was in astral mode at the time he threw the potion at her.
He was vanquished in the episode "Something Wicca This Way Goes...?" when he absorbed the Nexus into his body and the Charmed Ones cast a banishing spell to destroy it, thus destroying Zankou in the process.