Secret Service (Fallout 2)

The United States Secret Service was a United States federal government law enforcement agency, operating under the auspices of the Enclave following the Great War and the organization succeeding the American government. The Secret Service was reformed, tasked with protecting the government (most notably the President), though their activities will occasionally include being deployed on delicate missions to the mainland (such as silencing a Brotherhood outpost or state-sanctioned assassinations).  

Frank Horrigan, during his tenure as the Presidential bodyguard, would be considered a part of the Secret Service.