DSS (Detached Special Secretary) James Angleton is a character in the Laundry Files, his first appearence is in The Atrocity Archives.
He is a gaunt man with parchment-like skin, gleaming skull and a tiny chin. His ice-blue eyes have the nasty habit of seeing right through you, and are known to instantly silence lesser beings and employees.
His “public” code name is ANGLETON, just to piss off the USA secret services, and possibly to be a play on "the many angled ones" of which he is an embodiment. He is also associated to the code name TEAPOT when it comes to him being the Eater of Souls.
Not much Nothing is known of Angleton's past, but none in the Laundry seem to remember times he wasn't there "since forever". Bob is fairly certain he has seen pictures with Angleton in the background from around WWII, but Angleton doesn't seem to have aged since then.
More of his background is classified under The Fuller Memorandum
Years of experience (exactly how many is unknown) have made Angleton unfazeable. Not even the imminent end of the world will rouse him to more than a brisk, business-like efficiency. Coupled with his bone-dry (some say dessicated) sense of humor, Angleton is good, if unnerving, to have on your side.