Gaines Ruger Donoho was an American painter.

Gaines Ruger Donoho was born on December 21, 1857, in Church Hill, Mississippi. He grew up on his father Robert's plantation in Church Hill, Mississippi, until the elder Donoho was killed during the American Civil War. One of his mother's relatives, General Thomas H. Ruger (1833–1907), had them moved to New England with the rest of her family. He was trained as a painter at the Art Students League of New York in New York City and spent eight years in Paris.

He practised as an Impressionist, Symbolist and Tonalist painter in Manhattan. In 1891, he moved to East Hampton, where he continued to paint. He is best known for his landscape and garden paintings, some of which are reminiscent of Claude Monet's Giverney garden paintings. Additionally, he also did some drawings.

Some of his work is exhibited at the Metropolitan Museum of Art in Manhattan, Brooklyn Museum in Brooklyn, New York City and at the Mississippi Museum of Art in Jackson, Mississippi.

He was married to Matilda Ackley Donoho. He died on January 28, 1916, in New York City.After Donoho's death, Matilda Donoho sold the Long Island property to the Childe Hassams - good friends.