Darien Fawkes is an agent with The Agency.
From Wikipedia: "The plot revolves around Darien Fawkes, a thief facing life imprisonment who is recruited by a spy agency that is constantly short on funds, and given the power of invisibility via implantation of a special "Quicksilver gland" in his head. The gland allows Fawkes to secrete a light-bending substance called "Quicksilver" from his pores and follicles. The substance quickly coats his skin, hair, nails, clothes, and whatever he is carrying, and renders him invisible. He can consciously release the Quicksilver, which then flakes off and disintegrates. However, the Quicksilver gland was sabotaged at its creation by scientist Arnaud DeFehrn to release a neurotoxin that accumulates in the bloodstream and causes intense pain, followed by antisocial behavior and psychosis. The host requires regular doses of "counteragent" to keep him sane and healthy, which is controlled by the government agency."