Slavs
Slavs can be further grouped by religion. Orthodox Christianity is practiced by the majority of Slavs. The Orthodox Slavs include the Belarusians, Bulgarians, Macedonians, Montenegrins, Russians, Serbs, and Ukrainians and are defined by Orthodox customs and Cyrillic script as well as their cultural connection to the Byzantine Empire (Serbs also use Latin script on equal terms). Their second most common religion is Roman Catholicism. The Catholic Slavs include Croats, Czechs, Kashubs, Moravians, Poles, Silesians, Slovaks, Slovenes, and Sorbs and are defined by their Latinate influence and heritage and connection to Western Europe. There are also substantial Protestant and Lutheran minorities especially amongst the West Slavs, such as the historical Bohemian (Czech) Hussites.
Ukrainian language
During the Khazar period, the territory of Ukraine was settled by Iranian (post-Scythian), Turkic (post-Hunnic, proto-Bulgarian), and Uralic (proto-Hungarian) tribes and Slavic tribes. Finally, the Varangian ruler of Novgorod, called Oleg, seized Kiev (Kyiv) and established the political entity of Kievan Rus'. Some theorists see an early Ukrainian stage in language development here; others term this era Old East Slavic or Old Ruthenian/Rus'ian. Russian theorists tend to amalgamate Rus' to the modern nation of Russia, and call this linguistic era Old Russian. Some hold that linguistic unity over Rus' was not present, but tribal diversity in language was.