Demons were a class of creatures from the Age of Faerie who sought to ravage the land, kill all manner of life, and overrun the world without regard to the consequences. This put them in opposition with the Elves and other creatures of Faerie who sought to preserve and cherish the land and its life.
Eventually the conflict between the Faerie creatures intent on preservation and those bent on destruction culminated in a massive war. Those belonging to the former group were both unable and unwilling to annihilate their Faerie brethren completely, and so they ended the war by sealing the Demons within the Forbidding, a realm of darkness where only the cursed dwell.
Characteristics of the Forbidding
Originally described as a dark limbo world, the Forbidding is expanded in later stories and is described as a dark mirror world of the Four Lands, a desolate place where little grows and there is no sun, moon, or stars.
The Demons call themselves Jarka Ruus, which means "banished peoples" but which they translate as "the free peoples."
The Forbidding is maintained by the Ellcrys, a magical, sentient tree. The Demons remain locked away so long as the Ellcrys remains standing and does not fail. The Ellcrys was created through a combination of earth magic from the Bloodfire and Faerie magic involving the transformation of a young Elven girl called Aleia Omarosian into the tree. The Demons have attempted to escape the Forbidding on a number of occasions, usually when the Ellcrys begins dying and needs to be reborn.
War of the Forbidding
The Demons threatened the Four Lands when the Ellcrys began to die in the time of the Druid Allanon, and despite the united efforts of the Elves, Trolls, Dwarves, and the Bordermen of Callahorn, those battling the Demons nearly lost the war. The Demons had almost made it to the Gardens of Life where the dead Ellcrys resided when Amberle Elessedil, aided by Wil Ohmsford and the Rover girl Eretria, was transformed within the Gardens into a new Ellcrys, banishing the Demons into the Forbidding once more.
High Druid of Shannara
Dark Legacy of Shannara
Centuries after Amberle Elessedil was transformed into a new Ellcrys, the tree started dying again. Under the leadership of the Straken Lord Tael Riverine, the Demons attempted to escape the Forbidding once more. They were ultimately banished back to the Forbidding after Arlingfant Elessedil became the new Ellcrys. Just before they were banished, Grianne Ohmsford in her reincarnation as the Ilse Witch had killed the Straken Lord and taken his place as leader of the Demons. Because the Ilse Witch had chosen to become one of the Demons, she was banished along with them when Arlingfant was transformed.