Which alphabet is named for a Byzantine missionary saint to the Slavs?

The alphabet named for a Byzantine missionary saint to the Slavs is the Cyrillic alphabet.

Cyrillic is named in honor of Saint Cyril, the ninth-century Byzantine scholar and missionary who worked with his brother Methodius among Slavic peoples. Cyril and Methodius developed the earlier Glagolitic script for translating Christian texts, rather than creating Cyrillic itself.

Cyrillic emerged later in the First Bulgarian Empire, probably through the work of their students and followers at the Preslav Literary School during the late ninth century. Its letterforms were based largely on Greek uncial writing, supplemented with characters suited to Slavic sounds that Greek did not contain.

A common mix-up is to credit Cyril and Methodius directly with inventing Cyrillic. Their missionary and translation work inspired the tradition, but the script’s development is generally associated with their Bulgarian disciples. Cyrillic remains the writing system for languages including Russian, Bulgarian, Serbian, Ukrainian and Belarusian.