Answer: the Danubian Slavs of Eastern Europe
Step-by-step explanation:
Cyrill and Methodius are also known for creating the Slavic Alphabet (which would later evolve into the Cyrillic Alphabet still in use today) and translating the Bible into Old Bulgarian, spreading Christianity and Bizantine culture.
Though both were born in Thessalonica in the Bizantine Empire, they are considered Patron Saints of the Slavic people by the Catholic Church.