A Irmandade de Karn é Gallifreyanos, ex-seguidores das Pythias que governavam Gallifrey.
De aqui :
The Pythia was a name as much as a title of the matriarchal leaders of the planet Gallifrey prior to Rassilon. [...] Near the end of her reign, the last Pythia [...] sent her followers to the planet Karn, cursed Gallifrey with sterility and threw herself into an abyss below her temple. Pythia's followers would adopt the title of the Sisterhood of Karn. (PROSE: Cat's Cradle: Time's Crucible)
De aqui :
Karn was originally a colony of the old Gallifreyan Empire in the days before Rassilon. The Sisterhood of Karn were a remnant of the Pythias who once ruled Gallifrey before being expelled by the triumvirate of Rassilon, Omega, and the Other.