Originally named Peri Crystal, Peri was born in 1878. At the age of 27, she was taken to be used for testing of the new substance 'ADAM'. She was the fourth subject in the program, and thus named Subject Delta. The testing resulted in halted ageing, meaning that she was unable to grow old or die of natural causes. She was later involved in the events in Columbia, and afterwards was sent to Rapture. In Rapture, her DNA was used as a basis for some of the Little Sisters, making them her biological daughters. Eleanor Lamb was one of these Little Sisters. She allies herself with those who do the morally correct, like Jack and Subject Delta.