Nicholas I Mystikos or Nicholas I Mysticus (Greek: Νικόλαος Α΄ Μυστικός, Nikolaos I Mystikos) (852 – May 15, 925) was the Patriarch of Constantinople from March 901 to February 906 and from May 912 to his death in 925. Nicholas was born in the Italian Peninsula and had become a friend of the Patriarch Photios. He fell into disfavor after Photios' dismissal in 886 and retired to a monastery. Emperor Leo VI the Wise retrieved him from the monastery and made him mystikos, a dignity designating either the imperial secretary or a judicial official.