당신 can find out what happened to him if 당신 read the comic book Serenity: Those Left Behind. It shows why Book left the ship, why 오소리 wasn't in the movie and Mingo and Fanty were and resolves the Hands of Blue plotline.
I really never thought about what became of Badger. I did, however, recognize the actor, who has been in a lot of TV shows--Leverage, Burn Notice and others. He was a familiar face.
