Cyril Leo Heraclius, Prince Toumanoff (Russian: Кирилл Львович Туманов; 13 October 1913 – 4 February 1997) was a Russian-born American historian and genealogist who mostly specialized in the history and genealogies of medieval Georgia, Armenia, Iran and the Byzantine Empire. His works have significantly influenced the Western scholarship of the medieval Caucasus.
Cyril Toumanoff was born in Saint Petersburg into a family of the military officer of the Russian army. His father came of the princely family of Tumanishvili from Georgia, whose ancestors had emigrated from their original homeland in Cilician Armenia in the 15th century. This family is on the list of the Georgian princes that was attached to the Treaty of Georgievsk concluded between the Georgian king Erekle II and the Russian empress Catherine II in 1783. On December 6, 1850, the Tumanishvili were officially enrolled on the Russian Empire's list of Georgian princely families as knyaz Tumanov. Toumanoff's mother, Elizabeth Zhdanova, was a descendant of a number of Russian noble families, with genealogical ties with the Western European nobility.
Toumanoff's parents fled the October Revolution in St. Petersburg in 1917. His father joined the White Russian forces during the Russian Civil War, while his mother was put to death by the Bolsheviks. Cyril Toumanoff was initially sheltered by his maternal grandparents in Astrakhan. In 1928, Toumanoff's father was able to escape to the United States, bringing his son with him. Cyril Toumanoff attended the Lennox School which he graduated from in 1931 and went to Harvard. His educators John Coddington and Robert P. Blake helped him secure funding for travel to Brussels to study Armenology under Nicholas Adontz and then to Berlin, where he studied Georgian under Michael Tsereteli. During these years, Toumanoff converted to Roman Catholicism. A breach with his Orthodox Christian father ensued and was only terminated when the two reconciled at the latter's deathbed in 1943.