Robert K. Massie had studied European history at the University of Oxford as a Rhodes scholar. But it was neither academic research nor the pursuit of literary glory that led him to the stacks at New York Public Library devoted to Russian history, where he embarked on the intellectual journey that made him perhaps the most popular historian of Czarist Russia, known especially for his Pulitzer-winning biography of Peter the Great.

Rather, Mr. Massie delved into the lives of the Romanovs because he had something in common with Nicholas II and Alexandra, the last emperor and empress of Russia: Like them, he had a hemophiliac son. Theirs was Czarevitch Alexei, heir apparent to the throne before the family was executed by the Bolsheviks in 1918. His was Bobby, his first child, who was diagnosed with the incurable and often fatal blood-clotting disorder as an infant.

At the time, Mr. Massie was working as a book reviewer for Newsweek magazine. He began spending his lunch hours in the library, desperate to understand the disease that subjected his son to painful bleeding episodes, unremitting transfusions and periods in a wheelchair and leg ­braces.

“People write about what’s inside them,” Mr. Massie told the New York Times years later. He described his first book, “Nicholas and Alexandra” (1967), as “my attempt to write about Bobby’s illness in terms of another child. Nobody would show much interest in me writing about Bobby, but they were interested in the Czar’s son,” for whose benefit Alexandra had sought the supposedly healing services of the infamous monk Rasputin.

The volume sold more than 4.5 million copies and was adapted into a 1971 film that starred Michael Jayston and Janet Suzman in the title roles and was nominated for the Academy Award for best picture. The success helped pay for Bobby Massie’s medical expenses and established Mr. Massie as a leading chronicler of the Romanov dynasty.

Mr. Massie, who went on to publish sprawling biographies of Peter the Great and Catherine the Great as well as two in-depth naval histories of World War I, winning praise for the page-turning verve that he brought to his nonfiction, died Dec. 2 at his home in Irvington, N.Y. He was 90. The cause was complications from Alzheimer’s disease, said his wife, Deborah Karl.

Notable deaths in 2019: Elijah Cummings, Cokie Roberts, Toni Morrison and others we have lost this year

Don Imus | Don Imus, who spent more than half a century in radio and television skating along the edge of propriety and occasionally falling into the abyss of the unacceptable, died Dec. 27 at a hospital in College Station, Tex. He was 79. In a roller-coaster career in which he grew chummy with prominent politicians, repeatedly got suspended or fired for offensive cracks, abused drugs and touted health foods, Mr. Imus won a loyal following, made millions and transformed himself from a bad-boy DJ into a host whose program became a nearly mandatory stop for presidential candidates. Read the obituary (Richard Drew/AP)

Robert Loomis, Mr. Massie’s editor at Random House, once described Mr. Massie to the Times as an “amateur” historian, likening him to fellow Pulitzer Prize winners Edmund Morris, a biographer of Theodore Roose­velt and Ronald Reagan; and Daniel J. Boorstin, a former Librarian of Congress and prolific author of social history.

It was a compliment — a statement of admiration for the expertise that Mr. Massie had cultivated largely on his own and his ability to make thrilling yarns from historical events that another writer might have rendered in turgid prose.

Mr. Massie’s talent, one critic wrote in the publication Booklist, lay in weaving “narrative histories so engaging that readers, losing themselves in the romance-novel story style, forget that they’re reading nearly 1,000 pages of nonfiction.”

“Peter the Great: His Life and World” (1980) came in at approximately 900 pages and chronicled the life of the late-17th- and early-18th-century czar who founded the city of St. Petersburg and whose innovations in education, technology and military capabilities made him known as the architect of modern Russia.

“There were glimpses of his character, stories and legends about him,” Mr. Massie told an interviewer, “but I couldn’t find any biography which really captured him. After thinking about it for a while, I thought I could try one.”

Reviewing the volume for the Times, Kyril FitzLyon, also a scholar of Czarist Russia, wrote that “it would be surprising if it did not become the standard biography of Peter the Great in English for many years to come, as fascinating as any novel and more so than most.”

The book received the 1981 Pulitzer Prize for history and was adapted into an NBC miniseries starring Maximilian Schell as the czar and Vanessa Redgrave as his half-sister, the regent Sophia.

Mr. Massie possessed the ability to see historical figures as human beings rather than names on a dynastic tree. In one of his naval histories, he described Queen Victoria of England, who outlived her husband, Prince Albert, by 40 years, as a bereft widow who consoled herself by holding his nightshirt as she went to sleep and keeping “a cast of his hand on her night table so that she might reach out and hold it.”

Mr. Massie thought of his four daughters, he said, when he wrote “Catherine the Great: Portrait of a Woman” (2011), an account of an obscure German princess who became empress of Russia in the late 18th century and was often ranked with Elizabeth I of England among the most influential women of European history.

“This whole story of how Catherine grew up, how she became what she eventually did become, was such an extraordinary revelation of character, especially for women,” he once told the publication the Nashville Scene. “Women have to go through extra effort to get to the top, even today.”

In his acknowledgments published at the end of the best-selling book, along with expressions of gratitude for his editor and relatives, he thanked Catherine herself.

“I must acknowledge the extraordinary pleasure I have had in the company of the remarkable woman who has been my subject,” he wrote. “After eight years of having her a constant presence in my life, I shall miss her.”

Robert Kinloch Massie III was born in Versailles, Ky., on Jan. 5, 1929. His father founded a school for boys, and his mother was a social activist who participated in causes including the racial integration of lunch counters.

Mr. Massie spent part of his youth in Nashville, becoming captain of his high school football team. He received a bachelor’s degree in American studies from Yale University in 1950 before receiving a Rhodes scholarship.

His first job in journalism was as a researcher for the political journalist Theodore H. White at Collier’s magazine. After Newsweek, Mr. Massie wrote for the Saturday Evening Post before striking out as a freelancer.

Having served in the Navy during the Korean War, he turned to maritime history when he decided that he “had done enough about Russia.” His books on that subject included “Dreadnought: Britain, Germany, and the Coming of the Great War” (1991) and “Castles of Steel: Britain, Germany, and the Winning of the Great War at Sea” (2003).

But there could never be enough about Russia, and in 1995 he wrote “The Romanovs: The Final Chapter,” capitalizing on public fascination with the identification in 1993 of remains belonging to Nicholas II and his family. For years rumors had swirled about the possibility of surviving Romanov heirs. Mr. Massie visited the laboratory in Siberia where the bones were held and touched Nicholas’s skull.

Mr. Massie’s first wife, the former Suzanne Rohrbach, was also a Russian scholar and became an influential adviser to Reagan on Soviet matters. Together the Massies wrote “Journey” (1975), about their son’s struggle with hemophilia. The marriage ended in divorce.

In 1992, Mr. Massie married Karl, a literary agent. In addition to his wife, of Irvington, survivors include three children from his first marriage, Robert Massie IV of Somerville, Mass., Susanna Thomas of Harrodsburg, Ky., and Elizabeth Massie of Pelham, N.Y.; three children from his second marriage, Christopher Massie of Brooklyn, Sophia Massie of Poughkeepsie, N.Y., and Nora Massie of New Haven, Conn.; seven grandchildren; and a great-grandson.

While contending with the effects of hemophilia, Mr. Massie’s eldest son grew up to be an Episcopal priest, author, activist and Democratic politician.

Reflecting on history, and on its power to illuminate the present, Mr. Massie once remarked that he wished more people understood that “history is made by individuals.” One of them, he told the Times, was Czarevitch Alexei, “the little boy who was the most famous hemophiliac in history.”

CORRECTION: An earlier version of this obituary incorrectly described the relationship between Peter the Great and the regent Sophia. Sophia was his half-sister, not his wife.