Theoktistos or Theoctistus (Greek: Θεόκτιστος; died November 20, 855) was a leading Byzantine official during the second quarter of the 9th century and the de facto head of the regency for the underage emperor Michael III from 842 until his dismissal and murder in 855. A eunuch courtier, he assisted in the ascent of Michael II to the throne in 822, and was rewarded with the titles of patrikios and later magistros. He held the high posts of chartoularios tou kanikleiou and logothetēs tou dromou under Michael and his son Theophilos. After Theophilos' death in 842, Theoktistos became member of the regency council, but soon managed to sideline the other members and establish himself as the virtual ruler of the Empire. Noted for his administrative and political competence, Theoktistos played a