Kostia Vlastos (17 October 1883 – 28 October 1967) was a Greek of the diaspora, scion of a family of bankers.

Constantine Vlastos was born in Paris, as Constantine George Anthony Dimitrios Vlastos, but was widely known as Kostia Vlastos.^[1] His father Antonios Vlastos was born on 18 October 1858 in Galați, Romania, whose family name origins could be traced to the island of Chios.^[2] He was active in banking and was president of the Bank of Constantinople (Banque de Constantinople) of Andreas Syngros, Georgios Koronios and Stephanos Skouloudis. He later moved to Paris, where he managed the French broker house Comptoir d'Escompte. Antonios Vlastos was a great donor and one of the founding members of the Greek Philological Society of Constantinople, in 1861. His mother, Tarsi Vlastos (1860–1919), née Zarifi, was the daughter of the known Istanbul banker George Zarifis, from which Antonios Vlastos learned the banking business.

The Aéro-Club de France awarded Kostia Vlastos a spherical balloon (sphériques) pilot license (number 287) on 20 November 1913.^[3] When the 1912-13 First Balkan War was declared, the 29-year-old Constantine came to Greece and he volunteered in the Greek Army, thus providing his services for the liberation of the land of his ancestors. He initially took the rank of corporal and later that of sergeant. He joined the Army Company of Automobiles, apparently because of his ability to drive a car. During his service he was accompanied by his brother Stephen A. Vlastos (1885–1960),^[4][5] who was a war correspondent for the French newspaper Le Temps using the pseudonym Etienne Labranche.^[6]

Kostia Vlastos married Ludmila de Nittey, a Baltic Russian, born c. 1899 and died on 10 September 1989. The couple traveled three times to America in the 1930s and amongst their destinations was Honolulu, Hawaii, in 1932, according to the archives of Ellis Island, New York City.

Kostia Vlastos died in Bourron-Marlotte (Seine-et-Marne) on 28 October 1967 and was buried at the Russian Orthodox cemetery of Sainte-Genevieve-des-Bois outside Paris. His wife, Ludmila, was buried in the same tomb.^[1]