Successfully complete the game to have all classes unlocked during your next Campaign mode playthrough.

Successfully complete the indicated task to unlock the corresponding character in Hero mode:

Darth Maul: Get all four gameplay achievements.
General Grievous: Get all four gameplay achievements.
Jedi X2: Get both Instant Action achievements.
Mace Windu: Get two gameplay achievements.
Rahm Kota: Get two gameplay achievements.
Sith X1: Get both Instant Action achievements.