Rookie is Bowser's amnesiac alter ego and Popple's accomplice in Mario & Luigi: Superstar Saga and its remake, Mario & Luigi: Superstar Saga + Bowser's Minions. 
 Rookie's appearance is largely similar to his normal self's, though it differs in a few ways.  Rookie's personality is drastically different than Bowser's; he is extremely trusting, loyal, and ultimately submissive to Popple, whereas his normal self is arrogant and believes others are beneath him.