Russell Risley Sage (August 4, 1816 – July 22, 1906) was an American financier, railroad executive and Whig politician from New York, who became one of the richest Americans of all time. As a frequent partner of Jay Gould in various transactions, he amassed a fortune. Olivia Slocum Sage, his second wife, inherited his fortune, which was unrestricted for her use. In his name she used the money for philanthropic purposes, endowing a number of buildings and institutions to benefit women's education: she established the Russell Sage Foundation in 1907 and founded the Russell Sage College for women in 1916.

Sage was born at Verona in Oneida County, New York to Elisha Sage Jr. and Prudence Risley. His grandfather Elisha Yale Sr. was a construction contractor, and his uncle, Barzillai Sage, was the grandfather of railroad magnate Col. Ira Yale Sage of the Yale family. Russell Sage's nephew, Earl Chapin, also married to Cecilia A. Yale, sister of Col. John Wesley Yale, and mother of editor Charles Chapin.

Through his granduncles Capt. William Sage and Capt. Nathan Sage, distant cousins included Princess Kay Sage, wife of the Prince of San Faustino, Admiral Francis M. Bunce, Cornell benefactor Henry W. Sage, and Senators Henry M. Sage and Josiah B. Williams.

Princess Kay Sage, member of American royalty, was related by marriage to the Agnelli family, founders of Fiat S.p.A. and owners of Ferrari, with family members including Donna Virginia Bourbon del Monte, Princess Clara von Fürstenberg, Senator Giovanni Agnelli, minister Susanna Agnelli, and Italy's richest man, Gianni Agnelli of Villa Leopolda.

Sage received a public school education and worked as a farmhand until he was 15. He started as an errand boy in his brother Henry's grocery in Troy, New York. He had a part interest in 1837–1839 in a retail grocery in Troy, and in a wholesale store there in 1839–1857.

In 1841, Sage was elected as alderman in Troy. He was re-elected to this office until 1848, while also serving for seven years as treasurer of Rensselaer County. He was elected to the U.S. House of Representatives as a Whig. He was re-elected in 1854 and served from March 4, 1853, until March 3, 1857. He served on the Ways and Means Committee. Sage was the first person to advocate in Congress for the purchase of George Washington's plantation, Mount Vernon, by the government.

After retiring from politics Sage settled in New York City, where he engaged in the business of selling puts and calls, as well as short-term options known as privileges. He has been credited with developing the market for stock options in the United States and inventing the "spread" and "straddle" option strategies, for which he was dubbed "Old Straddle" and the "Father of Puts and Calls." He used the options to synthesize loans at a higher interest rate than state usury laws allowed, for which he was convicted in 1869 and fined $500, with a suspended jail sentence.

Sage bought a seat on the New York Stock Exchange in 1874, and became known as a financier. At the same time he saw the future of railroads, and secured stocks in western roads, notably the Chicago, Milwaukee and St. Paul Railway. He was president and vice-president for twelve years. By selling such investments, as the smaller roads were bought by major trunk-lines, he became wealthy. In his later years he was closely associated with Jay Gould in the management of the Wabash Railway, St. Louis and Pacific, Missouri Pacific Railroad, Missouri–Kansas–Texas Railroad, Delaware, Lackawanna and Western Railroad, and the St. Louis–San Francisco Railway, for which he was director of the corporations.