The American Protective League (1917–1919) was an organization of private citizens sponsored by the United States Department of Justice that worked with federal law enforcement agencies during the World War I era. Its mission was to identify suspected German sympathizers and to counteract the activities of radicals, anarchists, anti-war activists, and left-wing labor and political organizations. At its zenith, the APL claimed 250,000 members in 600 cities.

Thomas Watt Gregory was an American politician and lawyer. He was a progressive and attorney who served as US Attorney General from 1914 to 1919 under US President Woodrow Wilson.