Robert Alphonso Taft I (September 8, 1889 - July 31, 1953), of the Taft family political dynasty of Ohio, was a United States Senator and Presidential candidate in the United States Republican Party.

Robert Taft was the son of President William Howard Taft. Educated at Yale University, he got his law degree from Harvard University in 1913, and practiced law briefly in Cincinnati, Ohio, his family's ancestral city. During World War I he served on the legal staff of the Food and Drug Administration where he met the future president Herbert Hoover who became the idol of the young republican.

He began his elected political career in the Ohio House of Representatives, where he first won a seat in 1921, and served as Speaker of the House in 1926. In 1931 he moved to the state senate. He was elected to the first of his three terms as U.S. Senator in 1938; he was re-elected again in 1944 and 1950. He became chairman of the Senate Republican Conference in 1944.

As a U.S. senator, he was given the nickname "Mr. Republican"; he was the chief ideologue and spokesperson for the old-fashioned paleoconservatism of the Republican Party of that era. An isolationist, he strove to keep the United States neutral during World War II, and opposed conscription until the attack on the United States at Pearl Harbor in 1941. An active opponent of Franklin Roosevelt's "New Deal," he is famous as the co-sponsor of the Taft-Hartley Act.

He sought nomination as the Republican candidate for President in 1940, but lost to Wendell Wilkie; he again sought the nomination in 1948, but deferred to Thomas E. Dewey; and again in 1952, when he was initially favored to win the nomination due to his support from party insiders. However, after a tighly contested nominating convention, Taft was defeated by Dwight Eisenhower. The 1952 Republican National Convention is, as of 2004, the last major party nominating convention to require multiple ballots (three) to select a Presidential nominee. [Editing Note - Only one ballot was cast, in which Eisenhower was originally 9 votes short of winning until Minnesota changed its vote of 9 for Eisenhower and 19 for Stassen to 28 for Eisenhower. Nashorn, J. (1988) Choosing the Candidates – 1952. New York, NY: Garland Publishing, Inc. p 388]

Taft served briefly as Senate Majority Leader in 1953. He died later that year of cancer in New York City at the age of 63 and is buried at Indian Hill Episcopal Church Cemetery in Cincinnati. Robert Taft was the grandson of Attorney General and Secretary of War Alphonso Taft, son of President William H. Taft, father of Robert Taft Jr. (1917-1993), a former member of the United States Senate, and grandfather of Robert Alphonso Taft II, the current Governor of Ohio.