There's an interview with almost all you would want to know about this voice actor.
Game Spy have a detailed interview with Charles Martinet. It's a very nice read and includes how he became Mario, the games in which he has voiced characters, how much he likes working with Nintendo and much more.
Here's a small extract:
GameSpy: Have you met Nintendo's Shigeru Miyamoto (Father of Mario)?
Charles Martinet: PAPPA!!!!!!! That is what Mario says when he sees Mr. Miyamoto. Mr. Miyamoto is the most wonderful man! He is so nice; such a gentleman. It is hard to believe that the father of the video game industry could be so humble. If I ever created something that brought so much joy to so many people I would hope to be like him.
Now look up for the link and run and read the lot!