Robert Ferdinand Wagner I (June 8, 1877 – May 4, 1953) was an American politician. He was a Democratic U.S. Senator from New York from 1927 to 1949.

Born in Prussia, Wagner migrated with his family to the United States in 1885. After graduating from New York Law School, Wagner won election to the New York State Legislature, eventually becoming the Democratic leader of the New York State Senate. Working closely with fellow New York City Democrat Al Smith, Wagner and Smith embraced reform, especially to the benefit of their core constituency, the working class. They built a coalition for these reforms that embraced unions, social workers, some businessmen, and numerous middle-class activists and civic reform organizations across the state. Wagner left the state senate in 1918, and served as a justice of the New York Supreme Court until his election to the U.S. Senate in 1926.

As Senator, Wagner was a leader of the New Deal Coalition putting special emphasis on supporting the labor movement. He was a close associate and strong supporter of President Franklin D. Roosevelt. He sponsored three major laws: the National Labor Relations Act of 1935, the Social Security Act of 1935, and the Housing Act of 1937. Wagner resigned from the Senate in 1949 due to ill health, and died in 1953. His son Robert F. Wagner Jr. was Mayor of New York City from 1954 through 1965.