From Videogames & Cyberculture Reference
Big Daddy - Bioshock
Big Daddies are the heavily armoured mini-bosses that protect the wandering Little Sisters in Bioshock's city of Rapture. They are, like the Little Sisters, a tragic figure. Their humanity is all but erased by the extensive genetic modification, mechanisation and brain-washing inflicted upon them. The identities of the Big Daddies are never made clear, but it seems they would not have been volunteers, as the transformation into a Big Daddy was effectively a death sentence. Their suits are armour-plated diving gear, which allows them to withstand the deep ocean pressure as well as provide protection to the Little Sisters.
In the game, these mini-bosses are difficult to defeat, and the player is well-advised to take some time to plan an attack beforehand.