Successfully complete the indicated task to unlock the corresponding character:

Lou: Successfully complete Career mode to unlock Lou for purchase at the store 
for $15,000. Lou comes with his skeleton guitar.
Slash: Defeat Slash in the Boss battle in Career mode to unlock him for 
purchase at the store for $10,000.
Tom Morello: Defeat Tom Morello in the Boss battle in Career mode to unlock 
him for purchase at the store for $10,000.