Dark Energy, as he was referred to by the Indoctrinated and other servant factions, played a pivotal role in The Reaper War. Dark Energy served as the current Overlord of the Reaper forces during this current on going Cycle of Extinction.
Every 50,000 years, a new Overlord is chosen to lead the Reapers in their purge. The Overlord has to exhibit exceptional leadership skills and extensive knowledge and intelligence. Once one is chosen, they will spearhead the purge. The Overlord is the first one through the Citadel Relay, or in this case, the Far Rim Relays. The Overlord also has to show that he puts the other Reapers before himself, and will not go mad with power, since the Overlord is usually gifted with more powerful mass effect cores and weaponry, it is tempting to use this power to subvert the other Reapers. In this cycle, Dark Energy was chosen, mainly because the previous Overlord was a close ally of it. Dark Energy was known to be unforgiving, ruthless, and abusive to the other Reapers. He was also a young Reaper, many believed it to be too young. Dark began killing all Reapers who stood between him and the destruction of the galaxy.
Dark Energy had several run-ins with the SSV Pegasus, and its captain, Ambrose. Ambrose even had several direct encounters with the Reaper on several occasions, he even led a supposed suicide mission to board the Reaper and destroy its mass effect core. However, the mission was unsuccessful after the Alliance got in the way. Even though Dark Energy technically won every battle with the Pegasus due to being so much superior to other Sovereign-class Reapers, it still left every battle heavily damaged. The Pegasus had left Dark Energy weakened, and easy prey to the other Reapers, who had effectively labeled it a tyrant that had gone mad with power. An attack was launched on Dark Energy, an attack that Downfall instigated.
Dark Energy managed to kill several of his brethren before retreating to the Galactic core, here, Downfall finished him off, it is then that Downfall took control of the Reapers. Dark had not been the first to go rampant, there had been others, and the only way to relieve an Overlord of their pride and arrogance was death, as they knew that Overlords were the most powerful Reapers, and no organic weakling had a chance of killing even a normal Reaper.
- "I will not stand by as these foolish mortals desecrate our relics with their disease ridden bodies."
- "Your decay is a sign of weakness. Organic life as a whole is weakness. It weakens the universe, taints it."
- "Your very existence offends me. I will not stop until this Galaxy is ours once again."
- "The Reapers are fools. They think that by dethroning me they shame me. No, now that I've gone... I can hurt you."
- "The Reapers are over. When this universe burns, I will erect a pantheon of power so great, and so bright, that it will burn the eyes of the weak shut, it will singe the skins of the old gods, of the old machines, and the new will rise. Machines will die, organics will die, and only gods will remain, with me as their immortal deity. So sad, I don't know whether to be amused by, or to pity your ignorance, you have already lost and you can't even comprehend it, can't even begin to imagine it... just how frail you really are."