Big Daddies (originally named Protectors, and occasionally referred to as Mister Bubbles, or Mister B, 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, though still heavily spliced. Their primary purpose is to protect Little Sisterswhile they escort them around Rapture. If all of the Little Sisters have been either harvested or saved in a level Big Daddies will wander to a vent like usual and bang on it. However, a Little Sister will not come out, causing the Big Daddy to groan in frustration and bang again before letting out a sad moan and walk away in an attempt to find another Little Sister.
Aside from the Alpha Series, Big Daddies communicate by uttering 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 bioluminescent chemical substance which filled the helmet, displaying its state of emotion or mind. The Big Daddy has three different colors he will display.
- Green indicates the Big Daddy is hypnotized and friendly. This state can be seen here.
- Yellow indicates awareness but indifference to his environment, however, will react to people near him by shoving them, if the Big Daddy has a Little Sister with him and the player continuously stands in his way, the Big Daddy will become enraged in order to protect the threatened Sister.
- Red indicates rage towards assailants.
The surviving Alpha Series from BioShock 2 are in a permanent state of wrath due to prolonged separation from their Little Sisters. This excludes subjects Delta and Sigma owing to their unique circumstances.
He made his appearance during the final battle in the movie Ready Player One.