Forrest Gump turned 20 this summer, and this video from the auditions is making the rounds. At that point, the character didn't have a southern accent. It seems Hanks already has the part, and it's the other actors who are auditioning. 

If you like a good screen test, here are some famous actors auditioning for roles they didn't get, like Tom Selleck as Indiana Jones and Kurt Russell as Han Solo.