Sleeper Hit: The first film. It had tested horribly and Universal delayed it for a year to do reshoots. When it opened, it was expected to die a quick death against Scooby-Doo and Windtalkers. However, reviews and word-of-mouth turned out to be quite positive and it managed to gross over $100 million at the box office.
Star-Making Role: Matt Damon has mentioned that despite getting wildly critical acclaim for previous movies, it wasn't until he proved to have Box Office clout that film offers really started to show up.
Under Age Casting: Julia Stiles played Nicky Parsons, one of Jason Bourne's field handlers on an extremely sensitive mission and apparently has beyond Top Secret clearance given what she is involved in (monitoring all of the Treadstone field agents). In other words, significantly more dangerous to the Agency than Bourne is if she screws up, or if something was missed in her vetting and she is less than 100% loyal. When The Bourne Identity was released, Stiles was a very young looking 21. There's an attempted Hand Wave in The Bourne Supremacy when Nicky explains her cover was an exchange student studying in Paris.