10 Changes The Simpsons Hoped You Wouldn’t Notice
6. Hi, I'm Fat Tony, You Might Remember Me From...
Joe Mantegna IS Fat Tony. In fact, Joe Mantegna may fight you if you try to say otherwise. He based on the voice of the gangster on a member of his own family and has often, 'jokingly', referred to himself as fiercely territorial of the character. So, this makes this switch in the voices all the stranger - yet there certainly is a reason.
Show runners Bill Oakley and Josh Weinstein were huge fans of Phil Hartman and wanted to give him as much to do as possible on the show whenever they could. Therefore, the episode A Fish Called Selma was written to feature Troy McClure in a large role, so that Hartman would be able to dominate the episode in terms of 'voice' time.
Jeff Goldblum also guest stars, and had to rerecord his lines because the episode ran overlong - that's how much they wrote for Hartman.
There seems to have been a cheeky attempt to give him even more to do in the episode. In the scene where Troy McClure enters the DMV, the other characters react to his appearance. Specifically, they comment on the rumours surrounding his paraphilia fetish. It is Fat Tony who begins to explain what this means, only to be cut off.
But the fun fact - Mantegna did not voice Tony in this scene. That's Hartman, talking about Troy!