Cyrill was a scholar, theologian and linguist. He went on a mission to the Arabs and later became professor of philosophy at Constantinople.

In 862, when the ruler of Moravia (today in the area of Czechoslovakia) wanted to oppose East Frankish ecclesiastical influence and asked Constantinople for help, the patriarch Photius sent Cyrill as missionary.

Cyrill used the Slavonic language in the liturgy and he created the Cyrillic alphabet in order to prevent Jewish and Arab influences from infiltrating the Balkans. The Cyrillic alphabet is still in use in Russian and a number of other Slavic languages.