Cosmas of Aitolia was an eighteenth-century Greek hieromonk who, over roughly two decades of itinerant preaching, became the most influential missionary and educator among the Orthodox Christians of the Ottoman Balkans. Born around 1714 in the village of Mega Dendron near Thermo in Aetolia, he was given the worldly name Constas. After early studies under the archdeacon Ananias Dervisanos, he went to Mount Athos, where he attended the school at Vatopedi under teachers who included Eugenius Voulgaris, was tonsured a monk at the Philotheou monastery with the name Cosmas, and was later ordained hieromonk. He is commemorated on August 24.
Having obtained a written blessing to preach from Patriarch Seraphim II of Constantinople, and afterward from his successor Sophronius, Cosmas left Athos around 1760 to preach the Gospel in the towns and villages of the empire. For roughly nineteen years he traveled almost continuously through Thrace, Macedonia, the Danube regions, Thessalonica, Akarnania and Aitolia, Epirus, the Ionian islands of Lefkada and Kephalonia, and southern Albania, addressing crowds too large for any church. According to the tradition he was accompanied at times by forty or fifty priests and served vigils in open fields and city squares before thousands of hearers.
Alongside his preaching Cosmas placed great stress on education, and is credited with founding a large number of village and town schools so that the Orthodox could read and understand their faith and Scriptures. From his own letter to his brother Chrysanthos it is reported that he established ten higher Greek-language schools and some two hundred elementary schools, for which he often secured both teachers and funds. For this work he is honored as a teacher of the nation and counted among the figures of the Greek Orthodox revival of the period.
On August 24, 1779, in his mid-sixties, Cosmas was seized by the Ottoman authorities and put to death near Kolikontasi (Kolkondas), in the Fier district of present-day Albania, by the mouth of the Seman river. His body was cast into the water and, according to the tradition, recovered after three days by a priest named Mark and buried at a nearby monastery. He was formally glorified by the Ecumenical Patriarchate of Constantinople in 1961, and his relics were distributed to various churches.