Konstantin Theodor (from 1917 to 1919, Graf von) Dumba (17 June 1856 – 6 January 1947), was an Austro-Hungarian diplomat serving as its last accredited Ambassador to the United States and famous for having been expelled during World War I following accusations of espionage.

The Dumba, where of Aromanian[2][3] or Greek[4][5] descent, originally from the village of Vlasti in the Ottoman province of Rumelia, had emigrated and settled in Vienna in 1817.

[8] On 4 March 1913, Dr. Dumba was appointed as the successor of Baron Hengelmüller von Hengervár, the long time ambassador to Washington D.C. and dean of the diplomatic corps.

A first controversy concerned the Austro-Hungarian government's offer of 'rehabilitation' to those of its citizens living abroad and who had fled to escape compulsory military service provided they returned home and served in the army.

In the note, Lansing charged the ambassador with espionage for having advocated that his government back 'plans to instigate strikes in American manufacturing plants engaged in the production of munitions of war'.

[12] He left the United States on 5 October and was allowed to pass unhindered through the Entente blockade of the European continent and return to Vienna.

Count Tarnowski von Tarnów was named as his successor in November 1916 but never presented his credentials to President Wilson, thus making Dr. Dumba the last official ambassador of Austria-Hungary to the United States.