Due to their proximity to the emperor, the holders of the office had considerable power. Already under Emperor Leo VI the Wise (r. 886–912), a "mystikos" became Patriarch of Constantinople: Nicholas I Mystikos. Trusted by the emperors, the "mystikoi" are thus attested as occupying various important offices: at times they exercised the duties of a "protasekretis", various judicial duties, or served as heads of the establishment of the imperial bedchamber ("koitōn"). The office rose to particular prominence under Emperor Manuel I Komnenos (r. 1143–1180), when the "mystikos" was given charge of the imperial palace and the emperor's treasury, thus controlling not only the flow of salaries to the various imperial officials, but also the patronage and donations from the imperial purse to the Church. The office remained important in the 13th century, when at least one of its holders held the rank of "pansebastos". The title's functions at this time, however, are again unclear. The office remains attested up to the end of the Byzantine Empire in the 15th century.