A super-hero published by DC Comics.

Ray Palmer is the real name of the hero, the Atom. Palmer discovered a piece of a white dwarf star while a graduate student in physics. Palmer experimented with the white dwarf material, discovering a mechanism that enabled him to reduce both is mass and size. Fashioning himself a costume, Palmer became the smallest of heroes, the Atom.

The Atom served as a member of the Justice League fighting along side Superman, Batman, and other members. The Atom used his powers to visit sub-atomic worlds and to fight the forces of evil. Eventually, all of the Atom's adventures took a toll on his marriage and he and his wife divorced. Soon afterward, Palmer was believed killed in the Amazon jungle, but in fact, he was living with a group of aliens who had settled there. The aliens were six inches tall and had a primative society. Palmer helped them defeat their tyrant king and lead them for a time, until they were killed by corrupt government officials.

The Atom returned to the United States and was active for a time in his home of Ivy Town. Then during the Zero Hour crisis, the Atom was deaged to his teenage years. He joined the Teen Titans for a time and served as their leader in the field. Eventually, Palmer was returned to his normal age and returned to teaching in Ivy Town.

DC's first superhero called the Atom was a guy named Al Pratt. During the Golden Age of comics (in other words, around World War II), Al was a short kid (just 5' 1" tall) who got picked on and beat up a lot. He got tired of being the target of bullies and got some training from a boxing pro. He improved his physique and became an expert fighter; he had a shot at the professional boxing title, but chose to wear a funny costume and fight crime instead. Though he had no superpowers, he was quite successful and became one of the founding members of the Justice Society of America--of course, just about everyone else had powers, so he was just the short guy who was a good fighter, which wasn't that great for his confidence level. Later in his superheroic career, Al fought an atomic-powered enemy and, in the process, gained an "Atomic Punch"--a power that allowed him to hit things really, really hard.

Al retired from full-time superhero duties in the 1950s, but returned to the long-underwear game from time to time. He got married, fathered a son who was secretly kidnapped and eventually became a superhero called Damage (though Al and his son never met), and became the godfather for a boy who would eventually become a superhero called Nuklon. Al died during the "Zero Hour" crisis when a time-controlling villain called Extant aged a group of JSAers unnaturally.

The Atom was created by Bill O'Conner and Ben Flinton and made his first appearance in "All-American Comics" #19 in October of 1940.

Many thanks to Habakkuk, who provided additional sources for research. :)