Today, the Bulgarian Orthodox Church celebrates the Day of Bulgarian Patriarch St. Euthymius of Tarnovo. Euthymius was born around 1327 in a noble family. He received good secular education but his spiritual pursuits led him to the Kilifarevo Monastery, where around 1350 he became a monk. Later he resided in Constantinople and on Mount Athos for seven years.

Returning to his homeland, Evtimiy found seclusion to a cave not far from Tarnovo, where he founded the Holy Trinity Monastery. In 1371 he laid the foundations of the Tarnovo literary school, which is of great importance for the development of Bulgarian literature. He implemented an important spelling and language reform, which aimed at bringing unity between spelling and literary language. In 1375 he became Bulgarian Patriarch.