Misfits star Robert Sheehan is one of the more intriguing suggestions. Though he is Irish, he wouldn't be the first of his countrymen to make it big playing an American character, and there were clownish elements to his characterisation as Nathan in Misfits that would lend well to a young pre-transformation version of the Joker. It's unlikely that the show is going to play up the comedic elements of the character, unless just as slight link to what he will become down the line, but comic timing helps with villainous characterisation, particularly of even remotely grotesque characters. That is why Jack Nicholson's Joker worked, why Jim Carrey's Riddler worked (and yes, it did) and why Robin Williams is a far more engaging, creepy villain than anyone could ever have suspected from his more bloated comic performances. All three also trade heavily on charisma, and that is something that Sheehan has proved himself amply laden with: he is a genuinely likeable screen presence, which would lead to the irresistible possibility of a character who we fall in love with who turns out to be Batman's greatest ever villain. That is the sort of dynamic that audiences remember long after shows disappear.
