The American artist known for his abstract expressionist works in the mid-20th century is Jackson Pollock. Pollock is best known for his unique dripping technique, where he would create large-scale canvases by splattering or pouring paint in a frenetic manner. This style emphasized the act of painting as an integral part of the artwork itself and reflected the spontaneity of the creative process. His influential approach significantly changed the landscape of modern art, earning him a place as a leading figure in the New York School and profoundly impacting future generations of artists.