The Big Daddy are the protectors of the Little girls whom roam the halls of Rapture. The "Little Sisters" as their called, could be classified as vampires for their constant sticking of needles into dead bodies in order to drink the fluids inside, but that is aside the point, this is about their pedophilic guardians. If you want to purchase anything in the undersea lab that is Rapture, you must kill the small girls to obtain a sea slug in them. Muuurrrrdeerrr. There are two classes of Daddy's and they are the Rosie and the Bouncer, and they will be explained respectively.