Tom Kenny, the voice actor for SpongeBob, was not the original choice. Creator Stephen Hillenburg originally voiced the character during the pilot, but Kenny was hired after Hillenburg decided he wasn't the right fit.
Wow, I had no idea Stephen Hillenburg originally voiced SpongeBob! It's crazy how different the show could have been without Tom Kenny. His voice really became iconic and shaped the character. It's always fascinating to learn about the 'what could have beens' in the creative process.