Answer: converted Slavs to Christianity (especially western Slavs).
Explanation: founder of Bohemian (Czech) first dynasty (Premyslids) Borivoj received Christianity from their hands in Great Moravia. He was the first Czech duke who successfuly introduced Christianity to the Czech lands. Today they both are remembered in the Czech rep. because there is an official feast of Cyril and Methodius (July, 5). Cyril was older of both brothers and died in Rome (869 AD), younger Methodius became archbishop and died in Great Moravia. Both were of Greek origin.
