As far as movies go...Each joker has brought a special aspect to the screen...Cesar Romero was the goofball joker--the clown without the bit for the most part...more for fun than evil or really dark.Jack Nicholson was the gangster joker---a little nuts but mostly cruel and powerful...the crime boss with a touch of psychopath. Heath Ledger was the anarchist---He does the things he does simply because he can and they sound fun...intelligent and vicious with no constant plan or motive,Batman's nightmare one. Now Jared Leto will be the true sociopath it seems. All of these have basis in the comics depending on the writer so no offense but all the comics callers can now hush. The truth is each has,at least based on the trailer for Leto, owned their respective Jokers. Romero was an absolute goof when he played the Joker...you were never sure if he was a criminal or an idiot sometimes but it was fun. Nicholson's "Wait til they get a load of me" line was absolutely spine chilling in its awesomeness. And the level of amazing Ledger brought to the character can't be denied....ever. But regardless of what you think of Leto, be honest with yourself at least....his lines in the trailer were not only well written but believable and thrillingly done.Even those that think he will suck based on other works will have to see the movie because those lines....even if they are the best he has in the movie...tap into the core of the darkest images of Joker. Now that that has been settled....History for Ledger's version of Joker...... Well...If y'all remember right at the end of Batman Begins, Gordan was already talking about the new guys flair for the dramatic so 5 is out....The rest are all possible...black ops,goverment erasure of identity is plausible enough with a mental breakdown ending that career and starting a new one.To be honest though I think the best for that character would have to be he doesn't know. He is intelligent and vicious but not really cruel...he is a good fighter,can use weapons and explosives,tactically sound but if you think about it today so are alot of gangmembers.I know..the Joker...the Jason Bourne of the crime world.