Augustinas Voldemaras (April 16, 1883-December 16, 1942) was a Lithuanian nationalist who served as the country's first prime minister 1918, and again from 1926 to 1929.

Voldemaras was leader of the far-right Clerical Party and the "Iron Wolves" movement, inspired by Italian fascism. He returned to power in 1926 as head of a military coup that deposed prime minister Mikolas Sleževičius and ruled together with Antanas Smetona as virtual dictator of the country. He was an unpopular leader, but survived an assassination attempt in Kaunas in 1929. Later that year, while attending a meeting of the League of Nations, he was ousted in a coup by President Smetona, who ruled as dictator until the Soviet invasion in 1940.

On two occasions, Voldemaras attempted to overthrow the government and return to power: in 1931, for which he was acquitted, and in 1934, for which he was sentenced to twelve years in prison--he was pardoned four years later, in 1938, to mark the twentieth anniversary of Lithuania's independence, and sent into exile. He disappeared c. 1942, and it was only later that it was learned he had died in a Soviet prison.