It has been proven many times the Joker needs Batman to function. The original Batman. No replacement will do for him. Going Sane showed him actually becoming sane after he thought he managed to kill him. Death in the Family (and Batman #663, for example)  strongly hints he  knows Wayne is Batman.

So now that they're claiming Wayne is done being Batman (Batman R.I.P), what do you think the Joker will do? It would be foolish to brush aside his reaction, especially since there has been a lot of foreshadowing to imply the Joker will stop being Joker if there is no Batman anymore.

I say as long as there's a Batman there will always be a Joker.

Maybe Joker will find / create another batman

"Maybe Joker will find / create another batman"

I agree about him knowing who the man behind the bat is ^.^

I might be thinking too far ahead here or thinking of my own fun story arc in my head, but I think that if Batman ever tried to hang up his cowl & hood, that the Joker "might" give his replacement a chance & upon dissatisfaction, go after Wayne, not trying to kill him, but do whatever he can to get him back in costume. There are many ways he could go about this...drive the new Batman insane, or cause so much havock that he seems inadiquate & quits or is dethroned by Wayne, or he could just cripple or kill the guy, forcing Wayne out of vigilante retirement.  Heh, that's how I wish Batman Beyond had been...darker, with a more promanent Joker all the time trying to nuttify, test, & or kill the new guy.

Given his malevolence towards all the Robins, I'd say he precieves them as a Batman Replacement threat & I vaguely remember him having a shitfit with an imposter Batman once. & in Azreal he also showed dissatisfaction for stand-ins, telling him he wasn't worthy of his trap.

I seriously don't believe that the Joker would actually try to kill Batman until he was ready to die himself. He doesn't fear death, so he'll have to want to die. I'd like the Batman comics to go on forever, but when it finally does end (if in my lifetime) I'm hoping that they die at eachother's hands. The Joker's dependancy on Batman's existance & his being a masochist as well as a sadist suggests to me that that's his plan. That's why I liked Return of the Dark Knight so much ^.^

Azrael's what came to mind too. Can't remember if he ever had the time to encounter the Joker as Batman, but he is a perfect example (along with Robins) of how he reacts to substitutes.