Red Skull

In the 1997 DC/Marvel special Batman/Captain America, the Red Skull hires the Joker to steal an atomic bomb during World War II. Joker evades Batman, Cap, Bucky, and Robin and delivers it to the Skull, but is horrified when he learns that the Skull is a Nazi (saying "I may be a criminal lunatic but I'm an American criminal lunatic!"). When the Skull threatens to drop the bomb on Washington D.C., the Joker actually fights him in the plane's cargo bay. When Captain America and Batman take over the plane and bring it over the ocean, the two villains are dropped out with the bomb just before it explodes. Both Captain America and Batman are convinced the two are still alive somehow.