His All-Holiness Nicholas I Mystikus or Nicholas I Mystikos, (Greek: Νικόλαος Α΄ Μυστικός, Nikolaos I Mystikos), was the Patriarch of Constantinople for two periods: from March 901 to February 907 and May 912 to 925. He refused to recognize Emperor Leo VI’s marriage to Zoe Karbonopsina, his fourth.