Steampunk is a brass cyborg, and an active member of the Forerunners.
Steampunk is a changer with the ability to create complex weapons by making contact with machinery. He currently has several weapons, including Crimson King, a sword he created from a motorcycle, and Sapphire Rose, a revolver constructed out of Airsoft guns and a mini-freezer. He has also exhibited the ability to rev his weapons, as well as his own body, to power them up.
Steampunk does not have an official costume, but his brass limbs have been painted to give them a more rugged and coal-stained appearance.
Steampunk's first appearance was when he was under the control of an AI. After being defeated by Gacha and Incendiary, Steampunk was able to regain control over his body. He has been active member of the Forerunners ever since then.
The Forerunners seriously recruited this guy right after he went on a rampage!? I may have just lost all my respect for them. ~Anonymous