A better question is who the heck is this guy from War Games onwards that everyone kept saying was Black Mask, because he had bugger all in common with Roman, and was basically the Joker with a skull mask.
He and the Joker were both psycho, but other than that, different. The Joker isn't quite into long torture for it's own sake. Black Mask was also more of a straight up crime boss aside from the sadism.