William Conrad Gibbons, a Library of Congress researcher whose multi-volume “The U.S. Government and the Vietnam War” is regarded as one of the most comprehensive histories of that divisive conflict, died July 4 at his farm in Monroe, Va. He was 88.

The cause was complications from a stroke, said his wife, Patricia Gibbons.

Dr. Gibbons — officially a foreign policy expert in the library’s Congressional Research Service — was tasked in 1978 with a project that would occupy him, along with an uncounted number of other scholars, for decades. At the request of the Senate Foreign Relations Committee, he set out to compile a complete history of the Vietnam War.

It was a monumental job. The war had claimed the lives of an estimated 3 million Vietnamese and 58,000 Americans before its end in 1975. In the United States, the conflict left painful scars among antiwar activists, who felt deceived by their government, and among veterans who perceived that their sacrifices had gone unrecognized.

Dr. Gibbons’s opus, published by the Government Printing Office and the Princeton University Press beginning in 1984, would span more than 2,000 pages in four volumes chronicling executive and legislative policymaking from 1945 to 1968. A fifth volume was in progress at the time of his death.

William C. Gibbons, described as a “dean” of American researchers on the Vietnam War, died July 4 at 88. ( Family photo)

In his research, Dr. Gibbons pored over government records that filled thousands of boxes. In addition to mining documents from the White House, Congress, the military and the CIA, among other sources, he interviewed key government officials from the era. One was Robert S. McNamara, the defense secretary under presidents John F. Kennedy and Lyndon B. Johnson. McNamara, who died in 2009, was a principal architect of U.S. engagement in the war.

Dr. Gibbons collected no royalties for book sales, according to a profile in the Boston Globe, and he received little of the attention given to historians who write for popular audiences. But many such writers credited Dr. Gibbons with amassing and arranging the primary sources that helped form the foundation of their work.

Stanley Karnow, the Pulitzer Prize-winning historian whose 1983 book “Vietnam: A History” sold millions of copies, described Dr. Gibbons’s work as “one of the most valuable studies of the formulation of Vietnam policy during the Kennedy and Johnson administrations.” David Kaiser, a historian who taught at the U.S. Naval War College, once wrote in The Washington Post that Dr. Gibbons was “the dean of American Vietnam researchers.”

Lewis Sorley, a military historian who relied on Dr. Gibbons’s work, said in an interview with The Post that Dr. Gibbons was a “first-rate scholar.”

“Nowhere else has anyone assembled so much material from so many sources so authoritatively, accurately and of great utility to scholars,” Sorley said. Dr. Gibbons “demonstrated even-handedness, scholarly integrity . . . and diligence of the highest order,” Sorley added. “He was an archivist. He was a collector. He was an archaeologist of information on the Vietnam War.”

William Conrad Gibbons was born in Harrisonburg, Va., on Sept. 26, 1926. He was an Army veteran of World War II and received a bachelor’s degree in history and government in 1949 from Randolph-Macon College in Ashland, Va., and a PhD in politics from Princeton University in 1961.

He began his career on Capitol Hill, working as an aide to Sen. Mike Mansfield (D-Mont.), as a committee staff member and as an assistant to then-Senate Majority Leader Lyndon B. Johnson.

Dr. Gibbons worked in Washington for the U.S. Agency for International Development and in academia, including at Texas A&M University and Wellesley College in Massachusetts, before joining the Library of Congress in 1972, according to his family. He subsequently taught at George Mason University in Fairfax, Va.

He officially retired from the library in 1989 but continued working on the war history until 2004. The Globe reported that he did much of his writing using fountain pens and legal pads.

His marriages to Joan Lyon, Doris Scherz, Catherine Kennedy and Louise Erickson ended in divorce.

Survivors include his wife of 29 years, the former Patricia McAdams of Monroe; a son from his first marriage, Rob Gibbons of Albany, Calif.; a daughter from his second marriage, Frances Meier-Gibbons of Zurich; two children from his fourth marriage, Stephen Gibbons of Kill Devil Hills, N.C., and Gayle Gibbons Madeira of New York City; and two children from his fifth marriage, Ashley Gibbons of Monroe and Justin Gibbons of Indianapolis.

His other survivors include a brother, John H. Gibbons of The Plains, Va.; a sister, Elizabeth Reynolds of St. Petersburg, Fla.; and seven grandchildren.

Decades after the end of the Vietnam War, Dr. Gibbons found enduring significance in the conflict’s history.

“Our system is such that the president has the power to get us into these things, to get us trapped. We are still making foreign policy decisions without the necessary knowledge and with the arrogance that only comes from being American,” he told the Globe in 1998. “I think we are in for some very dangerous times in the days ahead.”