When you reach True Jedi Status in all 17 levels, the ? door opensin Dexter's Diner. Finish the mission for the following unlockables.

Darth Vader - Complete the mission behind the ? Door
Stormtrooper - Complete the mission behind the ? Door
Buy Princess Leia from Dexter - Complete the mission behind the ? Door
Buy Rebel Soldier from Dexter - Complete the mission behind the ? Door