He was a pioneer of Abstract Expressionism and one of the foremost exponents of action painting. His style is characterized by complex networks of swirling, interwoven lines of great delicacy and rhythmic subtlety. In the early 1940s Pollock moved from a vivid Expressionist style, influenced by Mexican muralists such as Siqueiros and by Surrealism, towards a semi-abstract style. The paintings of this period are colourful and vigorous, using enigmatic signs and mysterious forms. From 1947 he developed his more violently expressive abstracts, placing large canvases on the studio floor and dripping or hurling paint across them. He was soon recognized as the leading Abstract Expressionist and continued to develop his style, producing even larger canvases in the 1950s.