Cassius Marcellus Coolidge was an American artist, mainly known for his series of portraits Dogs Playing Poker. Known as "Cash" or "Kash" in his family, he often signed his work in the 19th century with the latter spelling, sometimes spelling his name, for comic effect, as Kash Koolidge.

Dogs Playing Poker, by Cassius Marcellus Coolidge, refers collectively to an 1894 painting, a 1903 series of sixteen oil paintings commissioned by Brown & Bigelow to advertise cigars, and a 1910 painting. All eighteen paintings in the overall series feature anthropomorphized dogs, but the eleven in which dogs are seated around a card table have become well known in the United States as examples of kitsch art in home decoration.