On July 26, 1908, the Federal Bureau of Investigation (FBI) is born when U.S. Attorney General Charles Bonaparte orders a group of newly hired federal investigators to report to Chief Examiner Stanley W. Finch of the Department of Justice. One year later, the Office of the Chief Examiner was renamed the Bureau of Investigation, and in 1935 it became the Federal Bureau of Investigation.

When the Department of Justice was created in 1870 to enforce federal law and coordinate judicial policy, it had no permanent investigators on its staff. At first, it hired private detectives when it needed federal crimes investigated and later rented out investigators from other federal agencies, such as the Secret Service, which was created by the Department of the Treasury in 1865 to investigate counterfeiting. In the early part of the 20th century, the attorney general was authorized to hire a few permanent investigators, and the Office of the Chief Examiner, which consisted mostly of accountants, was created to review financial transactions of the federal courts.

Seeking to form an independent and more efficient investigative arm, in 1908 the Department of Justice hired 10 former Secret Service employees to join an expanded Office of the Chief Examiner. The date when these agents reported to duty—July 26, 1908—is celebrated as the genesis of the FBI. By March 1909, the force included 34 agents, and Attorney General George Wickersham, Bonaparte’s successor, renamed it the Bureau of Investigation.

The federal government used the bureau as a tool to investigate criminals who evaded prosecution by passing over state lines, and within a few years the number of agents had grown to more than 300. The agency was opposed by some in Congress, who feared that its growing authority could lead to abuse of power. With the entry of the United States into World War I in 1917, the bureau was given responsibility in investigating draft resisters, violators of the Espionage Act of 1917, and immigrants suspected of radicalism.

Meanwhile, J. Edgar Hoover, a lawyer and former librarian, joined the Department of Justice in 1917 and within two years had become special assistant to Attorney General A. Mitchell Palmer. Deeply anti-radical in his ideology, Hoover came to the forefront of federal law enforcement during the so-called “Red Scare” of 1919 to 1920. He set up a card index system listing every radical leader, organization, and publication in the United States and by 1921 had amassed some 450,000 files. More than 10,000 suspected communists were also arrested during this period, but the vast majority of these people were briefly questioned and then released. Although the attorney general was criticized for abusing his power during the so-called “Palmer Raids,” Hoover emerged unscathed, and on May 10, 1924, he was appointed acting director of the Bureau of Investigation.

During the 1920s, with Congress’ approval, Director Hoover drastically restructured and expanded the Bureau of Investigation. He built the agency into an efficient crime-fighting machine, establishing a centralized fingerprint file, a crime laboratory, and a training school for agents. In the 1930s, the Bureau of Investigation launched a dramatic battle against the epidemic of organized crime brought on by Prohibition. Notorious gangsters such as George “Machine Gun” Kelly and John Dillinger met their ends looking down the barrels of bureau-issued guns, while others, like Louis “Lepke” Buchalter, the elusive head of Murder, Inc., were successfully investigated and prosecuted by Hoover’s “G-men.” Hoover, who had a keen eye for public relations, participated in a number of these widely publicized arrests, and the Federal Bureau of Investigation, as it was known after 1935, became highly regarded by Congress and the American public.

With the outbreak of World War II, Hoover revived the anti-espionage techniques he had developed during the first Red Scare, and domestic wiretaps and other electronic surveillance expanded dramatically. After World War II, Hoover focused on the threat of radical, especially communist, subversion. The FBI compiled files on millions of Americans suspected of dissident activity, and Hoover worked closely with the House Un-American Activities Committee (HUAC) and Senator Joseph McCarthy, the architect of America’s second Red Scare.

In 1956, Hoover initiated COINTELPRO, a secret counterintelligence program that initially targeted the U.S. Communist Party but later was expanded to infiltrate and disrupt any radical organization in America. During the 1960s, the immense resources of COINTELPRO were used against dangerous groups such as the Ku Klux Klan but also against African American civil rights organizations and liberal anti-war organizations. One figure especially targeted was civil rights leader Martin Luther King, Jr., who endured systematic harassment from the FBI.

By the time Hoover entered service under his eighth president in 1969, the media, the public, and Congress had grown suspicious that the FBI might be abusing its authority. For the first time in his bureaucratic career, Hoover endured widespread criticism, and Congress responded by passing laws requiring Senate confirmation of future FBI directors and limiting their tenure to 10 years. On May 2, 1972, with the Watergate scandal about to explode onto the national stage, J. Edgar Hoover died of heart disease at the age of 77.

The Watergate affair subsequently revealed that the FBI had illegally protected President Richard Nixon from investigation, and the agency was thoroughly investigated by Congress. Revelations of the FBI’s abuses of power and unconstitutional surveillance motivated Congress and the media to become more vigilant in the future monitoring of the FBI.