Nicholas Mystikos was a 9th-century philosopher and Ecumenical Patriarch of Constantinople who served two separate terms between 901 and 925. Born in the Italian Peninsula, he later became a close associate of Patriarch Photius I. After a period of monastic retirement, he was recalled by Emperor Leo VI to serve the imperial court. His leadership was marked by significant political involvement, including his role in the regency for the young Constantine VII and his diplomatic efforts to manage conflicts with the Bulgarian Empire.