A recent Interview by Newsrama, confirms that Jerry Robinson, the man who invent the Joker, is being discussed to play part in TDK as a consultant. Here's what the interview has to say:

NRAMA: What do you think of the Batman movies?

JR: I was more impressed with the last one [Batman Begins] than the others. I didn’t care for most of the others, mostly the writing and not necessarily the Acting. I hope the next one [The Dark Knight] will be good. I might be acting as a consultant on that.

NRAMA: Oh really?

JR: Possibly. That’s being discussed. So if that’s true, then I hope it’ll be the best one.

This is good news. I hope that Mr. Robinson is going to be given the consultant part on TDK.