Willem de Kooning (1904-1997) is best known for "action" paintings such as his "Woman" series. Below is the first of that line, done around 1950-52.
But this was not his only style. Unlike some others in the postwar New York School, de Kooning had received a fairly rigorous traditional basic art training, as his Wikipedia entry indicates. At the end of his active career, as his mind was deteriorating, he was painting curved dabs of paint on light-colored canvases. Unlike most other New York modernist painters active 1945-1960, de Kooning did not go totally abstract; his work always a connection (however slight) to the observed world, as is exemplified by "Woman I" above. As shown below, he experimented with abstraction a bit during the 1930s and began producing abstract paintings by the 1980s when he began its descent into dementia.
Between his student training in Rotterdam and the beginning of his fame in the early 1950s, de Kooning was busy experimenting with varieties of modernist stylistic traits, such as I discuss in Art Adrift, seeking to find his artistic "voice." Here are some examples: