Number Four

Battlestar Galactica 2004 Continuity
Battlestar Galactica 2004, Caprica and Blood & Chrome

Number Four, or Simon O'Neil, was a model of Humanoid Cylon. The initial prototype was developed not long after the end of the Cylon War in 1960, by a team of Thirteenth Tribe survivors dubbed the "Final Five" along with their first prototype Humanoid Cylon, a Number One. As with the other Humanoid Cylons, the Four prototype's consciousness was then replicated and installed into millions of cloned bodies, with their memories being able to be shared through a cloud server accessible either through "wiring in" or upon Resurrection. Because of this, there was little individuality among the millions of iterations of their respective models. During the Cylon Civil War, the Fours sided with the Ones and Fives.

Known Fours

• A Four lived on Gemenon as a doctor and got married to a young mother, Giana. During the Fall of the Twelve Colonies, he took his family to a spaceport to give them a chance of survival. When he was identified by Galactica-Cavil, he resisted orders to take part in mass-murder that would cost his family's lives, and instead airlocked himself while out of Resurrection range. Consequently, his unique experiences were not shared amongst the others.
• A Four lived on Caprica as the national Pyramid team's medic. He escaped the Fall when training took place in the mountains near Delphi and, when Caprica-Cavil insisted on not wiping out the whole resistance in one swoop, began slowly overdosing people on Morpha. He was identified as a Cylon after the attack on the Delphi Convalescent Institute and killed by the resistance.
• At least two Fours resided in Caprica's Delphi Convalescent Institute, where they operated a Farm. One or both directly oversaw the captive Lieutenant Kara Thrace while her ovaries were removed. One was killed by Lieutenant Thrace when she stabbed him with glass. Another was gunned down during the resistance's attack on the building.