The FBI was founded by U.S. Attorney General Charles Joseph Bonaparte in 1908, though it was later renamed and expanded under J. Edgar Hoover.

How the FBI Started

In 1908, President Theodore Roosevelt’s Attorney General, Charles Joseph Bonaparte, created a small investigative force inside the Department of Justice. He used Justice Department funds to hire about 34 special agents, many of them former Secret Service men and investigators, to handle federal investigations.

This new group had no official name at first, but it became known as the Bureau of Investigation (BOI) in 1909, when Bonaparte’s successor, Attorney General George W. Wickersham, formally established it.

The First Leader

The first chief of this new investigative service was Stanley W. Finch, who was appointed as Chief Examiner and later became the first “Chief” of the Bureau of Investigation. Finch is considered the first head of what would become the FBI, though the title “Director” came later.

From BOI to FBI

The agency grew slowly over the next decades and was renamed the Federal Bureau of Investigation (FBI) by an act of Congress in 1935. By that time, J. Edgar Hoover had been leading the Bureau of Investigation since 1924 and became the first Director of the FBI, shaping it into the powerful federal law enforcement agency known today.

So, while J. Edgar Hoover is often associated with building the modern FBI, the agency itself was founded by Attorney General Charles Joseph Bonaparte in 1908.

TL;DR
The FBI was founded in 1908 by U.S. Attorney General Charles Joseph Bonaparte as a small investigative force in the Justice Department; it was later renamed the Federal Bureau of Investigation in 1935 under J. Edgar Hoover.