From Bioshock - Wiki on Neoseeker

Big Daddies are powerful enemies in the world of Rapture. They live only to be the guardians of the Little Sisters as they collect ADAM.

Big Daddies are actually human beings who had their bodies embedded into large mechanical suits which give them agility and strength. Their minds have been erased making themselves useful for only protecting the Little Sisters.

The colors of the Big Daddies represent their status towards you.

• Yellow: The Big Daddy is neutral.
• Red: The Big Daddy is aggressive.
• Green: The Big Daddy is friendly.

[edit] Types Of Big Daddies

There are two types of Big Daddies.

[edit] Bouncer

Bouncer

The Bouncer is the standard type, having a large drill replacing one hand. In combat, it normally charges into the enemy and swings its drill around. It can stomp the ground, stunning the enemy and damaging them the same time.

[edit] Rosie

Rosie

The Rosie is the other type, holding a rivet gun. In combat, it usually sticks to long range attacks and throwing proximity mines towards the enemy.