Forget Cesar Romero: Mark Hamill ("Star Wars") has played The Joker longer than any other actor in the role. Years after his association with George Lucas, an older "Luke Skywalker" used his force to voice the iconic Bat-villain in hundreds of projects since 1992 (Hamill also voiced the Jokeresque Hobgoblin in the 90s "Spider-Man" cartoon).
One of the main questions raised by the Suicide Squad trailer is: who was the Joker torturing? It certainly looks like it was Harley. And those were almost definitely electro-shock paddles that attach to your temples that the Joker was holding.