Making his first appearance in Batman #59, Deadshot has since appeared as an assassin member of the Suicide Squad, Secret Six, and Checkmate. Lets just say the guy has good aim and he is next targetting the live action Arrow series and hoping that will launch him into mainstream villainy.
Deadshot's first onscreen appearance came in the Justice League episode The Enemy Below where he was a hired hitman assigned to kill Aquaman. He failed.
Deadshot returned in Justice League Unlimited in the series take on the Suicide Squad, the friendlier titled Task Force X successfully infiltrated the Justice League Watchtower to steal the Annihilator. Deadshot and his teammates were kept "honest" by the explosives implanted in their bodies.
Deadshot had the distinction of starring in the best (and perhaps only good) segment of the Batmanime Batman:Gotham Knight which was in fact titled Deadshot. In the story, the assassin was hired to kill Batman, a tough task.
The gun for hire returned once again in Superman / Batman Public Enemies hoping to cash in on the bliion dollar bounty on the Man of Steel. It only took him about 5 seconds to fail.
Smallville did a lot of villains well, Deadshot was not one of them. Before joining the Suicide Squad, Deadshot made his forgettable live action debut in the10th season episode Shield,where the steampunk cowboy wannabe tagged Clark Kent with a tracker.
In the Batman: The Brave and the Bold episode Night of the Batmen! Deadshot had the privilege of being dealt with by substitute Batman Green Arrow, perhaps a tease as the two characters are now slated to clash onscreen in the third episode of the 2012 Arrow series. Should be fun.