http://screenrant.com/simpsons-cast-salary-paid/

The Simpsons has been around almost 30 years. Is the show’s voice cast properly paid for their years of duty in Springfield?

A lot, and there's little hope for someone like me doing voice acting for the show. Some of the guest stars made their voices totally different than what I'm used to them sounding like such as Walter Stacy Keach who sounded nothing like he did when he played Mike Hammer. I finally got to watch the episode where I knew he'd be on it but hadn't been told ahead of time, so naturally I was disappointed when seeing his name in the credits. I wasn't into Mike Hammer, but my dad liked that show.
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