Saint Dionysius I (Russian: Дионисий); secular name: David (1300? – October 15, 1385) was a Russian Orthodox metropolitan in 1384–1385.
A native of the Duchy of Kiev as a young man David entered the Kiev Caves Lavra, where he was tonsured a hieromonk and given the religious name Dionysius. He is known to have spent a number of years living in a cave that he dug out himself on the banks of the Volga River not far from Nizhny Novgorod. Later, Dionysius founded the Pechersky Monastery on that same spot, which was dedicated in honour of the Ascension of the Lord. In 1374, he was consecrated the Bishop of Suzdal and won love and respect on the part of the locals.
In 1378, Dionysius was recommended as Metropolitan of Kiev by St. Sergius of Radonezh after the death of Metropolitan Alexius. However, Grand Prince Dmitri Donskoi had his own candidate – a priest by the name of Mikhail (Mityaya). Dionysius was one of a number of bishops at the council who opposed Mikhail, who was suspected of heresy (Strigolniki). If elected, Mikhail wanted to introduce a new way of enthroning the Metropolitan at home, in Russia, rather than traveling to Constantinople to be installed by the Ecumenical Patriarch (at the time, Russia was not yet an church). In 1379 Dionysius went to Constantinople carrying a protest against the choice of Mikhail addressed to the Patriarch. Mikhail was afraid that Dionysius would get the patriarch's blessing and followed him to Constantinople. However, Mikhail died on his way there and one of his accompanying clergymen, Archmandrite Pimen, reached Constantinople (Slavonic: Tzargrad) before Dionysius and was named Metropolitan of Moscow and All Rus' in place of Mikhail.