Medieval (9th century)
Feast: February 14
To preach the Gospel in Slavic, he first had to invent an alphabet. So he did.
The Slavic peoples of Moravia had no written language. Prince Rastislav asked Constantinople for missionaries who could teach Christianity in a tongue his people actually spoke, because the German clergy preaching in Latin weren't getting through. The emperor sent two brothers from Thessaloniki: Constantine (he took the name Cyril only on his deathbed) and Methodius. Constantine was the scholar — he'd debated Muslim theologians at the caliph's court and had already learned Hebrew and Arabic. But Slavic had no script. So before he could translate a single verse of the Gospel, he sat down and created one. The Glagolitic alphabet — ancestor of Cyrillic — was designed from scratch to capture sounds that Greek and Latin couldn't represent. Then the brothers got to work translating the liturgy, the Psalms, and the Gospels. The German bishops were furious. Preaching in the vernacular threatened their political control over Moravia, and they accused the brothers of heresy — everyone knew, they argued, that God could only be worshipped in Hebrew, Greek, or Latin. Cyril and Methodius traveled to Rome to defend themselves. Pope Adrian II sided with them and authorized the Slavic liturgy. Cyril, already ill, entered a monastery in Rome and died there in 869 at forty-two. His last prayer asked God to protect the Slavic people. The alphabet he made is still used by over 250 million people.