American painter, a leader in the Abstract Expressionist movement first studied as a Regionalist painter at the Art Students League, New York under Thomas Hart Benton, also influenced by Mexican Muralist paintings and Surrealism.   Perhaps best known for his "drip and splash" style which emerged in 1947 when he abandoned the traditional easel in favor of fixing the canvas to the floor or wall and pouring or dripping paint from the can on to it.   Instead of using brushes he manipulated it with "sticks, trowels or knives" and often adding an admix of "sand, broken glass or other foreign matter".