Barnett Newman is considered one of the major figures in abstract expressionism and one of the foremost of the color field painters. Newman's mature work is characterized by areas of color pure and flat separated by thin vertical lines, or "zips" as Newman called them, exemplified by "Vir Heroicus Sublimis" in the collection of MoMA. Newman himself thought that he reached his fully mature style with the "Onement" series (from 1948) seen here. The zips define the spatial structure of the painting while simultaneously dividing and uniting the composition. Although Newman's paintings appear to be purely abstract, and many of them were originally untitled, the names he later gave them hinted at specific subjects being addressed, often with a Jewish theme. Two paintings from the early 1950s, for example, are called "Adam" and "Eve" (see Adam and Eve), and there are also "Uriel" (1954) and "Abraham" (1949), a very dark painting, which, in addition to being the name of a biblical patriarch, was also the name of Newman's father, who had died in 1947. Newman's late works, such as the "Who's Afraid of Red, Yellow and Blue" series, use vibrant, pure colors, often on very large canvases.