Patrice Lumumba: to the extent people today have heard the name, it evokes vaguely leftist memories. A postal clerk turned anti-colonial agitator, Lumumba was the first leader of the Congo after it became independent from Belgium, in 1960. He took the helm as prime minister with high hopes, only to watch his country almost immediately spiral into chaos. The army mutinied, Belgian troops intervened, and two rogue provinces broke off.

For help saving his fledgling nation, Lumumba approached the Soviet Union, asking for planes, trucks, and weapons. That turned out to be a fatal mistake, as it prompted the C.I.A. to help overthrow him, try to assassinate him, and play an accessory role in his murder, in 1961, at the age of 35.

In the decades after his death, the man was lost and the myth replaced him. The French philosopher Jean-Paul Sartre wrote a fulsome introduction to a book collecting Lumumba’s speeches. The Soviet Union named a university after him. Malcolm X praised him as “the greatest Black man who ever walked the African continent.”

Posters of the revolutionaries Che Guevara (of Cuba), Lumumba, and Thomas Sankara (of Burkina Faso) in the Congo in 1985.

Suspicions of C.I.A. involvement in Lumumba’s death only enhanced his appeal on the left. My neighborhood coffee shop in Brooklyn used to sell T-shirts with Lumumba’s face and those of other supposed victims of the agency under the heading The C.I.A.’s Greatest Hits. Like Che Guevara or Mao Zedong, in the afterlife he was reduced to a clean leftist symbol.

Malcolm X praised Patrice Lumumba as “the greatest Black man who ever walked the African continent.”

But as I learned while researching my new book, The Lumumba Plot, this was a caricature. In poring over forgotten legal testimony, private letters and diaries, government archives, unearthed diplomatic cables, and recently declassified C.I.A. files, I came to realize that not only was it inaccurate to call Lumumba pro-Soviet, it was in fact more accurate to call him pro-American.

That certainly wasn’t the way the U.S. government saw him, however. Most consequential for Lumumba was the opinion of Allen Dulles, the philandering, pipe-smoking director of the C.I.A. at the time. “It is safe to go on the assumption that Lumumba has been bought by the Communists,” Dulles said at a National Security Council meeting. “This also, however, fits with his own orientation.” He concluded that the Congo’s leader was “a Castro or worse.”

Lumumba in the Congo in 1960, the year he took office.

In fact, Lumumba explicitly rejected the nationalization of private industry. His vision of national success, pitched at campaign rallies, included sending promising Congolese youth to be educated at British and American schools. Perhaps most telling, Lumumba entrusted his country’s economic future to an American, signing a 50-year, $2 billion contract handing over all the Congo’s mineral and hydroelectric resources to Edgar Detwiler, a dazzling entrepreneur from New York. (Detwiler turned out to be a con man, and the deal was quietly shelved.)

For help saving his fledgling nation, Lumumba approached the Soviet Union, asking for planes, trucks, and weapons. That turned out to be a fatal mistake.

In July 1960, Lumumba traveled to the United States, desperate for American help in restoring order to his troubled nation. President Dwight Eisenhower was out of town, but Lumumba managed to obtain a meeting with Secretary of State Christian Herter. The meeting would become much mythologized, with one of the U.S. officials present, Douglas Dillon, claiming years later that Lumumba was “psychotic.”

Lumumba at the National Airport, in Arlington, Virginia, where he was greeted by Secretary of State Christian Herter on July 27, 1960.

But at the National Archives in College Park, Maryland, I found the actual transcript of the meeting, which showed that Lumumba was nothing of the sort. In fact, he was at pains to praise America. “The people of the Congo, even in their most remote villages, have faith in the United States,” he said. “We know that the United States is anticolonial.” At another point during his D.C. trip, Lumumba even called on American troops to intervene in the Congo—hardly the words of a man beholden to Moscow.

The idea that Lumumba would simply ditch his ardent anti-colonialism and let his country fall under Soviet domination struck him as preposterous, and so it should have struck everyone else. Blinded by Cold War paranoia, however, U.S. officials decided that this anti-Belgian agitator was a committed radical, no matter what he thought about America. For Lumumba, this miscategorization turned out to be fatal. In the weeks after his visit to Washington, Eisenhower made it clear he wanted Lumumba disposed of—orders the C.I.A. dutifully followed.

Stuart A. Reid’s The Lumumba Plot: The Secret History of the CIA and a Cold War Assassination is out now from Knopf