Planck made many contributions to theoretical physics, but his fame rests primarily on his role as originator of the quantum theory. This theory revolutionized human understanding of atomic and subatomic processes, just as Albert Einstein's theory of relativity revolutionized the understanding of space and time. Together they constitute the fundamental theories of 20th-century physics. Both have led humanity to revise some of its most cherished philosophical beliefs, and have brought about industrial and military applications that affect many aspects of modern life. (from wikipedia.org)