Big Daddies (originally named Protectors, and occasionally referred to as Mister Bubbles by Little Sisters) are genetically enhanced human beings who have had their skin and organs grafted into an enormous diving suit, with Alpha Series being an apparent exception to the grafting process but still heavily spliced. Their primary purpose is to protect Little Sisters while they escort them around Rapture. Aside from the Alpha Series, Big Daddies communicate by haunting sounds similar to that of whale calls. Alpha Series communicate with low, inhuman grunts and roars. For easier interpretation (as stated in the Deco Devolution art book), production model Big Daddies have a mind controlling, bio-luminescent chemical substance which was filled into the helmet to display what state of emotion or mind that it is in. Big Daddy helmets have three light colors: green indicates the Big Daddy is hypnotized and friendly, yellow indicates awareness but indifference to his environment, and red indicates rage towards assailants. If the first few attempts to drive away potential threats prove futile, Big Daddies will become enraged, unlike Alpha Series who always begin enraged. Big Daddies have become a staple in the BioShock games, becoming a mascot of sorts for the series.