“…he, a lumbering palooka in a foul-smelling diving suit…”
― Andrew Ryan

Big Daddies (originally named Protectors, and occasionally referred to as Mister Bubbles or Mister B. by Little Sisters and Metal Daddies by Splicers) are genetically enhanced human beings who have had their skin and organs grafted into an armored 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.

Big Daddies were originally created by Dr. Yi Suchong to serve as Rapture's maintenance workers, to help in later construction projects, and to do the menial work of Rapture that was not profitable:[2] Rosies riveted panels and windows while Bouncers drilled deep-sea rocks and minerals for further city expansion.[3]