The main character from BioShock 2.
Subject Delta (Symbol: Δ) is the protagonist of BioShock 2. Delta was the first successful Big Daddy subject bonded to a Little Sister. He has a Delta symbol on his suit, which is the fourth letter in the Greek alphabet, signifying Delta was the fourth counted test subject taken from Persephone for Alpha Series conversion at Fontaine Futuristics. Delta is also a symbol commonly used in mathematics to represent change or variation.