Actually Stalin was a Christian and even trained to become a priest, then used the methods of organised religion to oppress and murder his own people. He attacks the Church as it was a threat to his power but in WWII then supported and promoted Orthodox Christianity as motivation to fight the Germans. Even after the war Orthodox Christianity in the SU rapidly expanded again, with thousands of Churches reopening and as long as they didn't question the Communisty government they were left alone.
So yes, Stalin was a murderous arsehole of the highest order, but he was no committed atheist, so please get your facts right.