The legend is based on the facial similarity of both men, Stalin's official birthdate controversy (claims that he was born on 6 December 1878 instead of 21 December 1879,) and that the late Stalin era saw a resurrection of interest to the personality of Przhevalsky, numerous books and monographs were published in the Soviet Union and satellite Communist countries (which was a rare occurrence in regard to the Tzarist-era scientists,) Soviet encyclopedias portrayed Przhevalsky in sharp similarity to Stalin, which was rumored that in such a discreet manner Stalin was paying a homage to his alleged biological father.