Philadelphia Phillies Community: The Phillie Phanatic.

http://philadelphia.phillies.mlb.com/NASApp/mlb/phi/community/phi_comm...

This link offers a story called - The Phanatic Makes His Debut, which details information on the beginnings of the Phanatic. In addition, there is a wonderful photo gallery of the Phillie Phanatic in action.

Referenced in:
Onomastics (Ono-what?) of Baseball Team Names and Mascots: What's In a Name?