Zeistian Priests served as a clerical and judicial body during the rule of General Katana, as seen in various versions of the film Highlander II: The Quickening.
On the planet Zeist in centuries past, under the despotic rule of the Immortal General Katana, a council of three priests worked in concert with the general to administer the planet, and to act as a covert check upon Katana increasing further in power.
In particular, Katana's obsession with the rebellion opposed to his rule gave the priests an opportunity to seed the potential for the general's downfall, by way of the banishment of criminals and revolutionaries to the planet Earth. Once there, these criminals would be immortal, utterly immune to aging and most physical harm, and capable of one day returning to Zeist with their freedom restored.
General Katana was deeply opposed to this policy, but according to the second film, was forced to concede to the judicial verdicts of the priests. Among the convicts sent to Earth by the priests after trial were Connor MacLeod and Juan Sanchez Villa-Lobos Ramirez, who later proved to be instrumental in Katana's eventual defeat.
Differences Between Film Versions EditDuring the end credits of the film, the priests are credited as "Zeist [Justices]," even in The Renegade Version, the film's Director's Cut which eliminated the notion of an extraterrestrial planet altogether, and changed the setting of General Katana's world to that of planet Earth's own distant past. Additionally, they are referred to onscreen as "priests" by Michael Ironside's character, which reinforces their clerical nature in the storyline.
Consequently, other changes were made to the film's narrative, including the removal of all Zeistian exiles gaining immortality upon arriving on Earth (in the Renegade Version, all exiles in the future are already Immortals, and looked upon as "unholy"). The priests themselves are established in the revised cut as likewise being Immortals, as well as General Katana.