"Tom Hanks in Philadelphia. There were some peeks of his potential prior to that with Sleepless in Seattle and League of Their Own but other than that he was mostly in some comedies and “that guy from Bosom Buddies and Big and Turner and Hooch” (and some other things but generally just a goofy guy)
Then he immediately followed up Philadelphia with Forest Gump and Apollo 13 and Saving Private Ryan.
What a transformation."