The Atom introduced in Showcase #34 (1961) is physicist and university professor Dr. Raymond Palmer, Ph.D. (He was named for real-life science fiction writer Raymond A. Palmer, who was himself quite short.) After stumbling onto a mass of white dwarf star matter that had fallen to Earth, he fashioned a lens which allowed him to shrink down to subatomic size. Originally, his size and molecular density abilities derived from the white dwarf star material of his costume, controlled by mechanisms in his belt, and later by controls in the palms of his gloves. Much later, he gained the innate equivalent powers within his own body. After the events of Identity Crisis, Ray shrank himself to microscopic size and disappeared. Finding him became a major theme of the Countdown year long series and crossover event.
Showcase has been the title of several comic anthology series published by DC Comics. The general theme of these series has been to feature new and minor characters as a way to gauge reader interest in them, without the difficulty and risk of featuring “untested” characters in their own ongoing titles. The original series ran from March-April 1956 to September 1970 suspending publication with issue #93, and then was revived for eleven issues from August 1977 to September 1978.