Russell Alexander Alger (February 27, 1836–January 24, 1907) was a U.S. Senator from the state of Michigan.
Alger was born in Lafayette Township in Medina County, Ohio. He was orphaned at age 12 and worked on a farm support himself and two siblings. He attended Richfield Academy in Summit County, Ohio, and taught country school for two winters. He studied law in Akron, Ohio, and was admitted to the bar in March 1859. He first began to practice law in Cleveland and moved to Grand Rapids, Michigan, in 1860, where he engaged in the lumber business.
(4 June 1860 census shows him at age 26 as an attorney in Grand Rapids.)
He enlisted as a private soldier in the American Civil War in 1861. He was commissioned and served as a captain and major in the 2nd Michigan Infantry Regiment. On October 16, 1862 he was made Lieutenant Colonel of the 6th Michigan Cavalry. He was wounded at Boonesboro, Maryland, and on returning to his command took part with Sherman in the campaign in the Shenandoah Valley. For services rendered, that famous soldier recommended him for promotion, and he was brevetted major-general of volunteers.

After the war, Alger settled in Detroit as head of Alger, Smith & Company and the Manistique Lumbering Company. Alger was elected Governor of Michigan in 1884, serving from January 1, 1885, to January 1, 1887. He declined renomination in 1886 and was a presidential elector on the Republican ticket in 1888. Alger was appointed Secretary of War in the Cabinet of U.S. President William McKinley on March 5, 1897. On September 27, 1902, Alger was appointed by Michigan Governor Aaron T. Bliss to the United States Senate to fill the vacancy caused by the death of James McMillan. He was subsequently elected by the Michigan State Legislature to the Senate in January 1903. He served until his death in Washington, D.C. in 1907.

In 1900 he was granted membership in the Sons of the American Revolution by virtue of his descent from Freeborn Moulton.