Not to be confused with the tiny titan, Captain Atom first appeared in 1960's Space Adventures #33. Although currently a mainstay of the DC Universe, even getting his own book as part of the 52 book relaunch this past September, Captain Atom was originally a Charlton Comics creation (who incidentally was the inspiration for everyone's favorite naked blue guy, The Watchmen's own Dr. Manhattan)
While the title of "Captain" seems easy to come by for superheroes and villains (see Captains Marvel, Mar-Vell, Boomerang, Cold, Planet, and Kangaroo) Nathaniel Adam, like Captain America, was an honest to goodness military man. After being atomized, Captain Atom gained the ability to fly and manipulate radiation. The heavy hitter made his onscreen debut in 2004 on the Justice League Unlimited series premier. Later in the series, Superman and Atom would clash and come to blows in the episode Question Authority.
Captain Atom returned to screen in the 2009 Superman / Batman: Public Enemies direct to video movie. As a government sanctioned hero, Captain Atom led a team to hunt down vigilantes Superman and Batman. As in his first appearance in JLU, things did not go well for Atom as a ripped suit led to a massive explosion.
In 2010, during the series premier of Young Justice, Atom made a quick appearance as a core member of the series' Justice League, though CA promises to make more substantial appearances as the series continues.
In 2011, Captain Atom made his debut on Batman: The Brave and the Bold in the series' final season episode Powerless!
Although he began the episode fully charged and wearing his modern silver suit, though when his powers were stolen by Major Force, he was relegated to his "powerless" status. Paying homage to the character's roots, Atom (this time Allen Adam like the original Charlton character) donned a suit reminiscent of his original comic design. He also taught us to, "Be a hero by remembering you're not!"