Marcus Daniels worked as a lab assistant until an accident gave him the power of the Darkforce manipulation (the powers that fuel Cloak), energy blast, portal creation, and flight. The lab accident also caused him to become mentally unstable--going so far as to kill his boss (whom he blamed for the side-affects of his power) and the man who had replaced him when he had left work because of his accident. He also required a stabalizer for a time to keep his powers in check, and would sustain brain damage when his power was strained. He became constantly fatigued from the strain on his body of being a portal with the Darkforce Dimension.
Mayor Story Arcs
Becoming a Villain
After Nova defeated him he lost control of his powers and vanished into the Darkforce Dimension, but was rematerialized during an experiment at the Project: Pegasus research facility. Confused and delusional, he broke out three super-villains there for testing and depowerment: Moonstone, Electro, and Rhino. Confronted by the Avengers, Blackout and Moonstone escaped through a portal with the Negative Zone the lab had created (nearly setting off a nuclear explosion as a distraction).
In the Negative Zone, Moonstone (who was a gifted psychiatrist) helped him begin to overcome his insanity and gain more control of his powers. The Avengers tracked them down, though, but Blackout was able to open a portal to the Darkforce Dimension and then, with Moonstone's help, return to their home dimension. Moonstone had them arrive near Attilan to get more moonstones from the Inhumans, but Dazzler defeated them and they were sent back to Project Pegasus.
Siege on Avengers Mansion
A while later, Moonstone and Blackout escaped once more. Moonstone was able to get recruited by Baron Helmut Zemo into a new incarnation of the Masters of Evil, and brought Blackout with her. They had a plan to attack and invade Avengers Mansion and defeat every hero whom unknowingly stepped inside. Blackout was very impaired by this point (to the point where he was only responsive to Moonstone). Baron Zemo and Fixer took advantage of this difficulties. They were able to control his mind via technology. It is as of yet still unclear whether Moonstone wanted him to be so dependent on her, or whether she wanted Zemo to control him. However, during the final battle with the Avengers, Doctor Druid restored much of Blackout's mind via magic. Blackout then began resisting Zemo's control, and his brain hemorrhaged, leaving him virtually dead. The Masters of Evil had been defeated, but at the price of Blackout's life.
Some years later however Zemo, now part of the Thunderbolts, was able to use Blackout's body as a puppet for some time. He used it to his advantage in defeating advisorys of the Thunderbolts. It is unclear what has become of his body now, or whether his mind can be restored.
Projects and manipulates semi-black energy known as the darkforce. Marcus has the strength and agility of a normal human.