Russia as an Orthodox leading power, the Tsar as the designated heir of the Eastern Roman Emperors, protector and messianic savior of the "captured" Eastern Church from Ottoman rule – these ideas became topoi from the 17th century that shaped the self-understanding of the Russian monarchy as well as the perceptions of European diplomacy and the Sublime Porte. The author examines the genesis of this complex of ideas in Greek ecclesiastical scholarly circles, its dissemination, and its transformation, taking into account and reconstructing the changing contexts. Far from representing a specifically Eastern European development or a timeless Byzantine tradition, the phenomena studied belong to the shared heritage of early modern Europe.