Iapetos, the Black Knight, spirit of Vengeance.
The myth behind the name is that Iapetus or "Iapetos" as the Greek pronunciation, was one of the Titan gods, sons of Ouranos (Heaven) and Gaia (Earth). Led by Kronos, Iapetos and his brothers conspired against their father, preparing an ambush for him as he descended to lie with Earth. Krios, Koios, Hyperion and Iapetos were posted at the four corners of the world where they seized hold of the Sky-god and held him fast, while Kronos, hidden in the centre, castrated him with a sickle.
Oh, and why the big f**king gun... BECAUSE REASONS!