Gregory of Sinai the Younger

Saint Gregory of Sinai, the Younger (Serbian: Григорије Синајски Млађи; late 13th- and early 14th-century) was the founder of Gregoriou Monastery at Mount Athos. The Serbian Orthodox Church as well as all the other co-religionist national churches celebrate his altar feast date of 7 December each year.

Source: Wikipedia — Gregory of Sinai the Younger (CC BY-SA 4.0)