John Edgar Hoover was born on January 1, 1895, in Washington, D.C. After graduating high school, he worked at the Library of Congress while taking night school classes at George Washington University Law School, eventually earning his LLB (bachelor of laws) and LLM (master of laws) degrees there.

In 1917, the year the United States entered World War I, Hoover passed the bar and obtained a draft-exempt position as a clerk with the Department of Justice.

Appointed as a special assistant to Attorney General A. Mitchell Palmer in 1919, Hoover began assembling information about tens of thousands of political “radicals,” using military and government intelligence, police investigations, private detectives, informants and many other tools–some of dubious legality–that he would put to effective use throughout his long career.

On January 2, 1920, Hoover’s division of the Bureau of Investigation (it wouldn’t be known as the FBI until 1935) carried out simultaneous raids in several major cities, arresting thousands of suspected Communists, anarchists or other radicals.

Initially hailed as a success, the so-called Palmer Raids were soon criticized by many for violating the civil liberties of thousands of Americans. Palmer eventually resigned in disgrace, but Hoover emerged relatively unscathed, despite his role in planning and executing the raids.

In 1921, Hoover was named assistant director of the bureau. Three years later, after President Warren G. Harding died of a heart attack and the emergence of the Teapot Dome scandal, his successor Calvin Coolidge named a new attorney general, Harlan Fiske Stone.

In May 1924, Stone fired the Bureau of Investigation’s director and appointed second-in-command Hoover as acting director. At the time, Hoover was just 29 years old.

Against the background of Prohibition (passed in 1920), organized crime thrived in the United States, with gangsters competing against each other for the profitable market in bootleg liquor.

And during the Great Depression, Hollywood and much of the American public romanticized gangsters and notorious outlaws like John Dillinger, Bonnie Parker and Clyde Barrow, “Baby Face” Nelson and George “Machine Gun” Kelly as heroes for their defiance of authority.

But Hoover made his FBI into the antithesis of this defiance, and a formidable symbol of law, order and morality. His agents–nearly all of them white, college-educated men–became known as “G-Men” (for Government Men), a moniker used by Kelly, who during his arrest reportedly said “Don’t shoot, G-Men, don’t shoot!”

Hoover also set out to reform the scandal-tarnished Bureau of Investigation into a more effective, professional investigative force. He fired sub-par investigators and instituted a rigorous hiring process and a strict code of conduct for all agents.

He also created a new Identification Division, tasked with handling the FBI’s growing fingerprint files and gathering prints from law enforcement agencies nationwide, and pioneered the bureau’s technical laboratory to perform sophisticated forensic analysis.

As the public face of the war on crime in the 1930s, Hoover became the ultimate G-Man in the public imagination. President Franklin D. Roosevelt gave the FBI a sweeping mandate to investigate fascism and communism in the United States, which Hoover used to increase domestic surveillance (including wiretapping).

He also kept tabs on a growing list of people he considered “subversives,” which would eventually include such famous figures as:

During World War II, Hoover’s bureau took much of the responsibility for investigating espionage at home as well as abroad, as the Central Intelligence Agency (CIA) did not exist at the time.

Once World War II gave way to the Cold War, Hoover turned his attention back to his lifelong obsession: the war on communism. The FBI went to work rooting out Soviet spies and dismantling their espionage networks, aggressively prosecuting accused spies like Alger Hiss and Julius and Ethel Rosenberg.

After the rise and fall of McCarthyism, Hoover reemerged as the nation’s leading anticommunism crusader. On the now-discredited theory that communism was linked to homosexuality, the FBI compiled vast files of suspected or known homosexuals within the U.S. government.

Ironically, rumors that Hoover himself was a closeted homosexual–and had a sexual relationship with his close friend and right-hand man at the FBI, Clyde Tolson–had swirled since the 1930s.

Despite Hoover’s widely rumored homosexuality, and his reputed penchant for cross-dressing, becoming one of the best-known aspects of his life, no hard evidence supports the idea that Hoover had a sexual relationship with Tolson–or anyone else, for that matter.

Apart from the fact that Hoover was particularly close to his mother, and until her death in 1938 lived with her in their family home, his personal life has remained shrouded in secrecy.

In the 1960s, Hoover’s FBI investigated leaders of the civil rights movement, which he believed was intimately connected to communism.

Hoover also compiled a considerable file on President John F. Kennedy, including his extramarital affairs and alleged Mafia connections, and he fought regularly with Robert Kennedy, JFK’s brother and attorney general, who attempted to exert greater control over the FBI’s activities.

At Hoover’s request, Robert Kennedy did authorize unlimited electronic surveillance of Martin Luther King Jr., and the FBI recorded much of the civil rights leader’s work and personal life.

After the assassination of John F. Kennedy, President Lyndon B. Johnson relied on Hoover more than ever and ordered him to crush the Ku Klux Klan in the South. Though Hoover might have retired at the then-mandatory retirement age of 70 in 1965, Johnson waived that law, and Hoover stayed in office.

Despite Hoover’s longtime personal friendship with President Richard M. Nixon, his leadership came under threat at the outset of the 1970s, as his enemies within the White House plotted to replace him–and an ambitious subordinate, Bill Sullivan, angled for his job.

Fearing Hoover still had the power to bring down the government, Nixon backed down from firing him in early 1972. Instead, Hoover fired Sullivan, appointing in his place an FBI veteran named Mark Felt (who would later become famous as “Deep Throat,” the main source for the Washington Post reporters who broke the Watergate scandal).

Early on the morning of May 2, 1972, Hoover died in his sleep at the age of 77. In the days after his death, President Nixon reportedly directed staff at the Justice Department to obtain the voluminous “secret” personal files Hoover kept in his office.

But by the time they got there, Hoover’s personal secretary had destroyed all the files, according to her boss’ instructions.

After Hoover died–and accusations mounted that his FBI had used illegal surveillance to spy on antiwar and political groups over the decades–the Justice Department would take steps to rein in the bureau. Crucially, they limited its directorship to a 10-year term, ensuring that no director after Hoover could exert so much power for so long.

Christopher Lydon, “J. Edgar Hoover Made the FBI Formidable with Politics, Publicity and Results,” The New York Times (May 3, 1972).

Kenneth D. Ackerman, “Five Myths About J. Edgar Hoover,” The Washington Post(November 9, 2011).

Biography: J. Edgar Hoover, PBS American Experience.

Tim Weiner, Enemies: A History of the FBI (Random House, 2012).

Curt Gentry, J. Edgar Hoover: The Man and the Secrets(W.W. Norton & Company, 2001).