A leading United States historian was forced to make a humiliating public apology yesterday after it was revealed that he had embellished his personal history with colourful but false roles in Vietnam and the civil rights struggle.

Joseph Ellis, winner of this year's Pulitzer Prize for history, admitted livening up his lectures and press interviews with fabricated tales of his own experiences.

His employers - Mount Holyoke, a prestigious Massachusetts women's college - were standing by him yesterday and the revelations were thought unlikely to lead to a withdrawal of his Pulitzer Prize, awarded for a book on the US founding fathers.

However, other historians and Prof Ellis's students expressed disillusion and disappointment yesterday that a renowned academic should have fallen prey to the temptation to fictionalise his past.

"Even in the best of lives, mistakes are made," Prof Ellis said in a statement issued by his lawyer. "I deeply regret having let stand and later confirming the assumption that I went to Vietnam. For this and any other distortions about my personal life, I want to apologise to my family, friends, colleagues and students."

The apology followed an investigation by the Boston Globe newspaper into his claims to have served as a platoon leader and paratrooper with the 101st Airborne Division from 1965 and to have later served on the staff of the US commander in Vietnam, General William Westmoreland.

In fact, the Globe found, Prof Ellis deferred his military service in 1965 in order to study at Yale, and later spent his active service teaching at West Point military academy. The historian's imaginary tour of duty in Vietnam is hardly uncommon.

As the trauma of the conflict has receded in the collective memory - replaced by a Hollywood-enhanced mystique - an increasing number of middle-aged American men in all walks of life have been found to have concocted a role for themselves in the jungles of Indochina.

Among other impostors unmasked in recent years have been the film actor, Brian Dennehy, who also offered a public apology after his claims to have been wounded while serving as a marine in Vietnam were denounced as phoney.

Glenna Whitley, who co-authored Stolen Valour, a book on the syndrome, said: "It's an odd kind of mystique. It's men of a certain age who are coming to the point in their lives where they're wondering, 'Did I do the right thing? Should I have gone?'"

Prof Ellis, who won a US National Book Award in 1997 for a biography of Thomas Jefferson, had made his Vietnam claims to Boston Globe reporters in 1997 and 2000, but had also used them to illustrate his lectures on the era. He had also claimed to have played an active role in the fight for civil rights for blacks in the southern states in the 1960s, and even fabricated accounts of being a successful college football player.

Joanne Creighton, the Holyoke College president, issued a statement yesterday, praising the history professor for his "great integrity, honesty and honour". She said: "Generations of Mount Holyoke women count him among their most inspirational teachers."

However, Arnita Jones, the head of the American Historical Association, said the Ellis case was disturbing. "Professors have an obligation in the classroom to be forthright and truthful about their own personal experiences," she told the Globe.

One of Prof Ellis's former students, Angel Kozeli, recalled his accounts of a massacre of Vietnamese civilians by US troops. She said she was baffled and dumbstruck by his admission that he had fabricated his personal history.

"He seemed so genuine," she said. "Perhaps it was a fantasy he came to believe himself."