Hofmann is one of the 20th Century artists whose influence on at and artists cannot be overstated. It isn't just his groundbreaking art. Hofmann was a teacher and his pupils (whether formal or not) are a who's who of the art world. He was also acquainted with the most important artists and art dealers of the early 20th Century.
Curiously he didn't have a major solo exhibition until he was around retirement age. Find out at hanshofmann.org.
Avery, although he frequently painted in a representational style, was incredibly important in abstract painting. Why? Simply put it was his use of color (although it is as much about the spatial). Critics of Avery, first, suggested his work was too abstract and then, as abstraction came into vogue, that it was too representational. These days, of course, this war between abstraction and representational art seems quaint. Most everyone agrees Avery was a true master of color.
The MOMA website has a great deal of information on Avery HERE.
Poons, born in Japan, intended to become a professional musician before changing gears and studying art at both the School of the Museum of Fine Arts (Boston) and the Art Students League of New York. His career seems to be based on periodic drastic changes to his style. There is a restlessness in his art--even work made recently. Look at his piece Arithmetic here (which is not done justice in a photograph).
Find out more about Poons at larrypoons.com.