Almost all of the members of the Czech and Slovak Orthodox Church were 20th-century converts from Roman Catholicism or Greek-Catholicism. The faithful included Czechs, Moravians, Slovaks and back then Rusyns (Carpatho-Ukraine was a part of Czechoslovakia up to 1945) who felt disenfrachised by the Catholic priests. The conversions and the formation of the Church itself were an attempt to return to Slavic roots and to the teachings of the Saints Cyril and Methodius who first converted Moravia & Slovakia in 863.
The faithful of the then Czechoslovak Orthodox Church were Czechoslovak patriots as well as pan-Slavs, and their ranks quickly grew from almost no Eastern Orthodox faithful to 145,000 by the 1931 census (including some 120,000 Ruthenes in Carpatho-Ukraine).
In 1942, the head of the church, Bishop Gorazd, was arrested, tried, tortured and executed by the Nazis. His offense was harboring the conspirators who had assassinated Nazi official Reinhard Heydrich. This involvement caused harsh reprisals for Eastern Orthodox faithful in German-held Protectorate of Bohemia and Moravia. Some 256 Orthodox priests and prominent believers were either executed or deported to slave labor camps in the Third Reich.
Following the end of the war, in 1945, the Czechoslovak Orthodox Church held a memorial service for Bishop Gorazd. Prominent citizens of Prague of all faiths paid their respects to the murdered cleric in the Orthodox Cathedral of Sts. Cyril and Methodius. He is now known as Saint Gorazd, recognized as a martyr by Orthodox Christians throughout the world.