Askold and Dir
Some Soviet historians (Boris Grekov, Vladimir Pashuto, Rybakov) argued that Christianity was adopted in the 9th century only by the Varangian elite of the Rus' Khaganate. That the fact of the first Christianization was obliterated so rapidly is explained by the 882 "coup d'état" that led to the downfall of the supposedly Christian Askold and the usurpation of power by the pagan Oleg. (But some sources noted that Oleg was a varangian too.) The first proponent of this theory was Vasily Tatischev who concluded that Askold and Dir had been murdered on account of their Christian views. He went so far as to style Askold "the first Russian martyr".