Atreus is a mobster who is in charge of the gun trade in Caprica City.
Sam Adama is running guns to Tauron to help his people in their new struggle against the corrupt Tauron government. Sam is shaking what guns he can off the streets. Atreus catches Sam in the act. He kills Sam's partner, Demos, but lets Sam go so he can send a message to the Guatrau not to muscle in on his gun business.
The Gautrau tells Sam he must avenge Demos' death alone, since he acted alone without the Guatrau's consent.
Sam discovers the U-87 robots' capabilities and and takes one with him to Atreus' hangout at the Skybar where Atreus and his friends are celebrating their victory over the Guatrau. The Cylon opens fire on the room and kills everyone except for Atreus, only wounding him. Sam toys with Atreus who thinks Sam will let him go. Instead, the cylon opens fire on Atreus and riddles him with bullets, killing him.