Big Daddy

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 Sisters while 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.