In Bioshock, a Rosie is one of two types of the Big Daddy types of enemies. For those unfamiliar with the game, Bioshock takes place in 1960 in a giant underwater city called Rapture that was built in the post WWII years. A Big Daddy is one of the many genetically modified beings you will find in the city; they tend to ignore the player unless you either attack them first, or attack the Little Sister they are guarding. The Little Sisters gather genetic material, ADAM, to fuel the underwater war machine in the city. The Rosie's choice of weaponry? A rivet gun.