In your Imperial Assault campaigns, the Rebel player(s) control heroes. Unlike the other characters in the game, heroes are allowed to perform multiple attacks each activation. They are also more difficult to defeat: they can rest, recovering strain equal to their Endurance. If they have less strain than their Endurance, they recover damage equal to the difference. Once they suffer damage equal to or exceeding their Health, they are not out of the game, but they do become wounded and flip their hero sheet to the other side. Each hero has their own unique deck of class cards that they can buy with XP gained from missions. Each hero also has their own special side mission which, if the Rebels win, grants them a reward card unique to that hero. They also have ordinary deployment cards for use in a Skirmish game, where they must follow all rules for normal characters, like attacking only once per activation.
Up to the release of The Bespin Gambit all heroes have certain characteristics in common. When the heroes become wounded they retain the same Health and Defense. The heroes will always lose 1 to their Speed and Endurance stats. The hero will also drop slightly in all three of their attributes (Strength, Insight, and Tech). Finally, almost all heroes retain their first ability when wounded and lose access to their last ability. In the rare case when a hero has 3 abilities they retain the first two when wounded. (The notable exception to this is Diala Passil whom has her retained ability swapped into the lower position as the result of a typo in the Core Set.)