Dr. Ferrell, who taught for many years at Indiana University and was considered one of the country’s leading historians, wrote more than 20 books and edited or collaborated on dozens of others.
Dr. Ferrell concentrated on the study of diplomacy early in his career. He wrote a biography of George C. Marshall, the World War II general who later served as secretary of defense and secretary of state, and in 1959 published “American Diplomacy,” an authoritative history that appeared in revised editions for decades.
He later wrote books on various aspects of the presidencies of Woodrow Wilson, Warren G. Harding, Calvin Coolidge, Herbert Hoover and Franklin D. Roosevelt, but he had a particular affinity for Truman, a fellow Midwesterner and piano player. He published 11 books about the 33rd president and was, historian Kai Bird wrote in The Washington Post in 1994, “probably as responsible as any academic for refurbishing Truman’s reputation.”
Truman became president in 1945 upon the death of Roosevelt — whose final year was chronicled in Dr. Ferrell’s 1998 book “The Dying President.” Late in 1951, amid the Korean War, Truman’s approval rating stood at an abysmal 23 percent, and he was widely considered a crude failure as a president who allowed Communism to sweep across Eastern Europe.
Dr. Ferrell was one of the first scholars to present a thorough reevaluation of Truman’s achievements. He gave the president high marks for leading the country through the end of World War II, the integration of the armed forces and the creation of the CIA — and for having a folksy optimism that connected with people throughout the country.
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Dr. Ferrell edited several volumes of Truman’s papers and in 1983 came across a cache of more than 1,200 previously unknown letters from Truman to his wife, Bess.
The Trumans’ daughter, Margaret Truman Daniel, believed her mother had burned the letters, but they were found in Bess Truman’s house in Independence, Mo., after her death in 1982. Dr. Ferrell was the first scholar to examine them in depth.
In 1983, he published more than 500 of the letters in “Dear Bess: The Letters From Harry to Bess Truman, 1910-1959.”
“This may be the frankest and most important presidential correspondence of this century,” he told the New York Times. “It is also a wonderful 19th century love story talking to the 20th century.”
Truman wrote to his wife every day they were apart, never failing to admire her appearance and to plead for more letters from her. In 1913, after she agreed to marry him, Truman wrote to his betrothed: “I know your last letter word for word. I read it some 40 times a day. Oh please send me another like it . . . You really didn’t know I had so much softness and sentimentality in me, did you?”
The wedding finally took place in 1919. In his letters, Truman confided everything to his wife, including his views of political figures and world leaders — and his sometimes retrograde views of African Americans and other minorities.
He was frank about his own shortcomings, calling himself “a failure as a farmer, a miner, an oil promoter, and a merchant but finally hit the groove as a public servant — and that due mostly to you and lady luck.”
Dr. Ferrell wrote other books about Truman, including a 1994 biography that had the misfortune of coming out two years after David McCullough’s Pulitzer Prize-winning biography.
In 1998, Dr. Ferrell published his account of Roosevelt’s final year, “The Dying President.” After interviewing some of Roosevelt’s doctors and reviewing medical records, he concluded, “The president, it now can be said, knew he was suffering from cardiovascular disease, knew he was seriously ill, and chose to keep that fact a secret.”
Historian John Lukacs, writing in the Los Angeles Times, called “The Dying President” “a revelation” and “also much more than that. It is concise, sparklingly well-written, bearing the marks of a master historian.”
Robert Hugh Ferrell was born May 8, 1921, in Cleveland. (He shared a birthday with Truman, who was born in 1884.) His mother had been a teacher, and his father was a banker who struggled to make a living during the Depression. The family moved throughout Ohio during Dr. Ferrell’s youth.
A talented pianist, he planned to become a music teacher when he enrolled at Ohio’s Bowling Green State University. After four years in the Army Air Forces during World War II, he returned with a new dedication to history.
He received two bachelor’s degrees from Bowling Green — one in education in 1946 and another in history a year later. At Yale University, he received a master’s degree in history in 1948 and a doctorate in 1951.
Dr. Ferrell taught from 1953 to 1987 at Indiana University, and the Society for Historians of American Foreign Relations named an annual prize in his honor.
His wife of 45 years, the former Lila Stout, died in 2002. Survivors include a daughter, Carolyn Ferrell of Ann Arbor, Mich.; and two granddaughters.
In 2000, the Chicago Sun-Times asked 50 distinguished historians to rate the best presidents in history. Using a variety of measures, including character, Dr. Ferrell ranked Truman second only to Abraham Lincoln. George Washington came in third in Dr. Ferrell’s rankings, and FDR was at No. 8.
“The judgment on character and integrity can make quite a difference,” Dr. Ferrell said. “In my own instance, I rate Franklin D. Roosevelt low in those qualities, because of his willingness to tell fibs and to turn on his supporters generally if the political equation made it convenient. This violates, I think, a political leader’s responsibility to be honest with friends and enemies alike and surely not to dissemble with supporters.”