Newton Diehl Baker Jr. (December 3, 1871 – December 25, 1937) was an American lawyer, Georgist, politician, and government official. He served as the 37th mayor of Cleveland, Ohio from 1912 to 1915. As U.S. Secretary of War from 1916 to 1921, Baker presided over the United States Army during World War I.

Born in Martinsburg, West Virginia, Baker established a legal practice in Cleveland after graduating from Washington and Lee University School of Law. He became a progressive Democratic ally of Mayor Tom L. Johnson. Baker served as city solicitor of Cleveland from 1901 to 1909 before taking office as mayor in 1912. As mayor, he sought public transit reform, hospital improvement, and city beautification. Baker supported Woodrow Wilson at the 1912 Democratic National Convention, helping Wilson win the votes of the Ohio delegation. After leaving office, Baker accepted appointment as Secretary of War under President Wilson. He was one of several prominent Georgists appointed to positions in the Wilson Cabinet.

Baker presided over the U.S. military's participation in World War I. He selected General John J. Pershing to command the American Expeditionary Forces, which he insisted act as an independent unit. He left office in 1921 and returned to BakerHostetler, the legal practice he co-founded. He served as an attorney in Village of Euclid v. Ambler Realty Co., a landmark case that established the constitutionality of zoning laws. He was a strong supporter of the League of Nations and continued to advocate American participation in the League during the 1920s. Beginning in 1928, he served as a member of the Permanent Court of Arbitration. He was a candidate for the presidential nomination at the 1932 Democratic National Convention, but the convention chose Franklin D. Roosevelt.