Originally Posted by Mister Meddle
So what if Nicholson wasn't as disguised as Ledger's Joker? The thing is he didn't need to. Nicholson naturally had a sinister look that was perfect for the role. As well as his natural devilish voice. Perhaps this is the reason everyone wanted him to play the Joker long before he agreed to the role. Everyone knew he was capable of playing a convincing psychopath that also had the perfect voice and look to go with it. Plus you can't go wrong with a comic accurate look.
That's also what I'm saying - Jack Nicholson did change his voice. It's more subtle than what Ledger did but it's still there. You just need to hear the change from his more normal-sounding voice as Jack Napier to Joker.
In fact, I heard Ledger had to work hard to not sound like Jack Nicholson.