The mystikos (Greek: μυστικός, "the secret one") was an important Byzantine office of the imperial chancery from the 9th through to the 15th centuries.
The office first appears in the reign of Emperor Basil I the Macedonian (r. 867–886), when it was held by Leo Choirosphaktes.
[2] Franz Dölger regarded the mystikos as the emperor's private secretary, while Nicolas Oikonomides considered him already at that stage as a judicial official.
[4] The office remained important in the 13th century, when at least one of its holders held the rank of pansebastos.
He was possibly the assistant of the mystikos, since he follows right after him in the list of offices of the Escorial Taktikon, written ca.