The FBI originated from a force of special agents created in 1908 by Attorney General Charles Bonaparte during the presidency of Theodore Roosevelt.
Roosevelt and Bonaparte both were "Progressives." They shared the conviction that efficiency and expertise, not political connections, should determine who could best serve in government. Theodore Roosevelt became President of the United States in 1901; four years later, he appointed Bonaparte to be attorney general. In 1908, Bonaparte applied that Progressive philosophy to the Department of Justice by creating a corps of special agents. It had neither a name nor an officially designated leader other than the attorney general. Yet, these former detectives and Secret Service men were the forerunners of the FBI.
Attorney General Bonaparte appointed a force of special agents within the Department of Justice. On July 26, 1908, Bonaparte ordered them to report to Chief Examiner Stanley W. Finch. This action is celebrated as the beginning of the FBI.
Both Attorney General Bonaparte and President Theodore Roosevelt, who completed their terms in March 1909, recommended that the force of 34 agents become a permanent part of the Department of Justice. Attorney General George Wickersham, Bonaparte's successor, named the force the Bureau of Investigation on March 16, 1909. At that time, the title of chief examiner was changed to chief of the Bureau of Investigation. Source: FBI