Nicholas I Mystikos or Nicholas I Mysticus (Greek: Νικόλαος Α΄ Μυστικός, Nikolaos I Mystikos; 852 – 11 May 925) was the Ecumenical Patriarch of Constantinople from March 901 to February 907 and from May 912 to his death in 925. His feast day in the Eastern Orthodox Church is 16 May.[1]