An organization of federal workers, or agents, designed to secure the US against security risks that disrupt the government somehow "clearing the picture" for other departments/agencies/forces or sending in their own forces for exigent purposes. They also have a nationwide web of phone/webtaps, informants, spies and undercover guys ("plants"). Founded in 1908 with the purpose of fighting crime more effectively nationwide, they eventually lasted through trying times such as the Prohibition, WW1/WW2 and 9/11 and continue their work today.
An agent: a suit with an signed ID. Usu. seen with a 9mm handguns, black Sedan and a red tie. *Some believe they are actually aliens.* ::GASP::