American painter associated with the New York school of Abstract Expressionism who is notable for his distinctly personal use of colour, often in brilliant bands or stripes.

Louis studied painting at the Maryland Institute, Baltimore (1929–33), and from 1937 to 1940 he worked as an easel painter in the Works Projects Administration (WPA) Federal Art program. His early work was Cubistic, but his style changed abruptly in 1952 following his exposure to the Abstract Expressionist paintings of Jackson Pollock. In 1953 he was deeply impressed by Helen Frankenthaler's method of staining an untreated canvas with poured paint, and his later work took the form of stained vertical waves of colour, of which “Iris” (1954) is an example. After 1961 he painted in striking parallel streams of colour that flowed across the bottom corners of his pictures. In his last works he used vertical, straight stripes of colour.