Sirius was once a great warrior, but fell in battle. He later woke in the labyrinth and has stayed alive by hunting the prisoners sent to the Dregg to seek the only means of escape, a Boom Tube.
Throughout his life in the dungeons, Sirius had encountered many sacrifices, but took a special liking to a young Scott Free - recognizing his good soul amongst the evil on Apokolips, and so allowed him to live.
Sirius is defeated by Orion many years later, and asks the Dog of War to liberate him from his prison by killing him. Before Orion is able to, Desaad attempts to kill Orion with an effluvia. However, Sirius is able to save Orion's life by getting to him to the Boom Tube before sacrificing his life.