The Cellar is an Intelligence agency of the U.S. government.
It is a very hush-hush one operating out of the deep basement, hence the name, of the NSA main building. It is known about by the leaders of the major alphabet groups in the American intelligence community but to most it is a complete unknown and to most who are aware of it, it is almost mythical so quietly and subtly does it usually operate.
The original purpose of the Cellar was really to watch the watchers but over time, as always, things change. It still maintains its primary role but after 9/11, the Cellar learned it had to take a bit more active role.
How big the organization is remains a mystery to even its own operatives as most are trained to work alone. Support staff is known to be fairly small because the mandate the Cellar has from the top allows it to call upon any of the other groups to handle logistics. If an agent needs a ride somewhere, there is one waiting. If warm bodies are required, the FBI or ATF or CIA or someone somewhere gets a call and people, usually in the dark as to what is going on or why, show up.
Heading up the Cellar is one man, an aging former soldier known as Nero. Mr. Nero to most as familiarity and Mr. Nero do not go together. He lives in the Cellar in special rooms created just for him. He has no friends or family nor any feeling of loss for not having them. He also has no vision for a Gestapo interrogator took that away during the latter days of WWII. He also has no voice box as years of chain smoking has taken much of his throat. What he does have is an incredibly keen intellect and an amazing ability to spot patterns. He is by no means perfect as he will be the first to admit but he is darn good. He is also close to death.
In the first of the two books that exist of the Cellar's activities, the main characters are not official operatives of the Cellar. One does not even know of its existance when things start getting heady. Nevertheless, both feel the string pulling done by Nero and the Cellar at just about every turn. They resent it, naturally, but that does not stop the yanking from going on. In the second, the inner workings of the Cellar become clearer but the string pulling and manipulation does not slow down at all.
Nero is a wonderful character to read and learn about. I cannot get enough of the woman only known as Neeley. Hannah Masterson is truly a joy to follow. And Gant is, well, Gant. You need to read the books to understand but once you do, you certainly will get what I mean.