Theoktistos was a prominent 9th-century Byzantine official who served as the primary regent for the young emperor Michael III from 842 until his death in 855. A highly influential courtier, he held several prestigious titles, including magistros and logothetēs tou dromou. He played a decisive role in the imperial administration, eventually consolidating power within the regency council to become the empire's de facto ruler. His leadership was characterized by significant religious and educational shifts, though his tenure ended abruptly when he was assassinated by the emperor's uncle, Bardas.