"The Joker" or just "Joker" ?

I'm watching The Dark Knight Returns Pt. 2 (which is awesome) and I noticed he is constantly reffered to as just "Joker".

Even on the talk show they introduce him this way. I've always heard people call him The Joker, but is there an official canon of what to call him?

They do say "the Joker" once or twice, actually. Sorry if this thread is kind of pointless but I was just wondering.