E. Howard Hunt, secret agent and dirty tricks expert, was the mastermind of the bungled Watergate break-in that brought down President Nixon in disgrace and precipitated America’s most notorious political scandal.

It was Hunt’s name and telephone number, found in the possession of one of the captured Watergate burglars, that proved to be the first thread connecting the operation to the White House and the CIA. Hunt, the most colourful of the conspirators, had recruited four of the five inept Cuban exiles who broke into the Democratic national headquarters at the Watergate complex on June 17, 1972. With his co-conspirator, G. Gordon Liddy, Hunt watched in horror from an adjacent building as the operation unravelled and heard the last radio transmission from the break-in team announce “they got us” as the police moved in.

Hunt set out to live the life he had imagined for himself, a glamorous career as an agent like the all-American heroes of his many spy novels. But in real life he was never much of a success. He was, said Samuel F. Hart, a retired ambassador who first met him in Uruguay, “totally self-absorbed, totally amoral and a danger to himself and anybody around him”.

“That fellow Hunt,” President Nixon muttered a few days after the Watergate break-in, “he knows too damn much.”

Hunt did not let loyalty to Nixon prevent him from pressing the White House for large sums of money for his defence and to pay the legal costs for the other arrested Watergate conspirators. A White House taped conversation that became a key piece of evidence for Nixon’s part in the cover-up recorded Nixon’s counsel, John Dean, declaring: “We’re being blackmailed — Hunt now is demanding another $72,000 for his own personal expenses; another $50,000 to pay his attorney’s fees.”

Facing impeachment for the Watergate cover-up, Nixon resigned on August 9, 1974.

In one of the many personal tragedies of his career, Hunt’s wife, Dorothy, was killed when a United Airlines airliner crashed in Chicago in December 1972. In her handbag she was carrying more than $10,000 in cash; this was generally assumed to be part of the hush money paid to Watergate defendants in an attempt to procure their silence regarding White House involvement.

In 1970 Hunt ended his long and somewhat chequered career with the CIA to concentrate on writing spy novels. He was recruited by Nixon’s special counsel, Charles Colson, to carry out dirty tricks and acts of political warfare from a clandestine office in the White House. He was taken on as a part-time consultant to the President for $l00 a day.

Hunt later described his capabilities: “I was trained in the techniques of physical and electronic surveillance, photography, document forgery and surreptitious entries into guarded premises for photography and installation of electronic devices — to put it unmistakably, I was an intelligence officer, a spy for the Government of the United States.”

Hunt’s first assignment from Colson was to get the inside story on the Kennedys — the involvement of President Kennedy’s Administration in the overthrow of the South Vietnamese President Ngo Dinh Diem and more details of Senator Edward Kennedy’s behaviour over Chappaquiddick.

Hunt was soon switched from this to collect damaging information on Daniel Ellsberg, a former Pentagon official who had leaked secret papers about the Vietnam War.

With the anti-war movement gaining strength, Nixon had become obsessed about official leaks, and the White House recruited a group of so-called “plumbers” to stop them.

It was decided to break into the Beverly Hills office of the psychiatrist treating Ellsberg to obtain personal information to discredit him. For the illegal break-in Hunt requested the CIA to provide him with a red wig, a false driving licence and devices to alter his voice and make him appear to limp. Although the burglary proved a failure and nothing damaging to Ellsberg was found, the plumbers, led by Hunt, then embarked on a career of White House-sponsored crime that led directly to Watergate.

Asked later what he had hoped to achieve by the Watergate break-in, Hunt said he was looking for evidence of illegal foreign contributions to the Democrat Party: “We’d heard rumours that both the Vietnamese and Fidel Castro were inserting funds illegally into the Democratic National Committee. And the idea was to look at the books. It didn’t seem like such a deal to me; you know I’d been doing that stuff for years, a black-bag job into other embassies.”

Everette Howard Hunt was born in Hamburg, New York, in 1918, the son of a lawyer and a classical pianist. He graduated from Brown University in June 1940, was commissioned in the US Naval Reserve and served as gunnery officer of a destroyer. After the war he received a Guggenheim Fellowship and then joined the Office of Strategic Services, the precursor of the CIA.

In a colourful career he served behind the lines in China, tried Hollywood screenwriting, served with Ambassador Averell Harriman in Paris working on the Marshall Plan, and from 1949 was involved in the Cold War. He served with the CIA in Vienna, Mexico City, Tokyo, Uruguay and Madrid, and planned operations in the Balkans and Guatemala.

He took credit for orchestrating a 1954 coup against Guatemala’s elected left-wing President Jacobo Arbenz and was involved in the hunting down and killing of Castro’s ally, Che Guevara, in Bolivia.

In 1961 Hunt was assigned to help to organise the disastrous Bay of Pigs invasion aimed at deposing Castro. His assignment was to create a provisional Cuban government to assume power once the CIA-backed Cuban exile army had invaded the island. He developed a deep contempt for President Kennedy for failing to send in US armed forces to rescue the invaders when they were surrounded by Cuban forces, and conspiracy theorists alleged that Hunt was later involved in the assassination of Kennedy.

Like many CIA agents, Hunt found that his career was undermined by the Cuban fiasco and he eventually retired, complaining that the agency was “infested” by Democrats. However, he became a legend among the right-wing Cuban exiles under his code name Eduardo, and it was from their ranks that he recruited the Watergate team.

Hunt spent 33 months in prison for his role in Watergate and was bitter that Nixon did not stand up for him. President Reagan rejected a request for a pardon for Hunt in 1983.

“I am crushed by the failure of my government to protect me and my family as in the past it has always done for clandestine agents,” he told the Senate committee investigating Watergate in 1973. “I cannot escape the feeling that the country I have served for my entire life and which directed me to carry out the Watergate entry is punishing me for doing the very thing it trained and directed me to do.”

His life in ruins, his wife dead and legal fees approaching $1 million, Hunt suffered a stroke, and whatever illusions he once had that his government would protect him were shattered. Standing before the judge who imprisoned him, he said he was “alone, nearly friendless, ridiculed, disgraced, destroyed as a man”.

Throughout his life he wrote about 80 spy novels and thrillers. The majority were published under a variety of pseudonyms. One of his leading spy characters was Peter Ward, who shared a similar career to Hunt and whom the author described as “the secret agent with the taste and the talent for fine living”.

Tad Szulc, a former New York Times reporter, in his book Compulsive Spy: The Strange Career of E. Howard Hunt wrote that Hunt was a relatively low-level CIA officer not well thought of by most of his colleagues and superiors.

Hunt was declared bankrupt in 1997, largely blaming Watergate fines and legal fees. A $650,000 libel settlement stemming from an article alleging his involvement in the assassination of President Kennedy was overturned, and he received no money.

Freed from prison on his 60th birthday, he moved to Miami where he married his second wife, Laura, a teacher, and started a new family.

Hunt’s last book, American Spy: My Secret History in the CIA, Watergate and Beyond, with a foreword by his old friend William F. Buckley, is about to be published.

Hunt is survived by his wife, the two daughters and two sons of his first marriage, and two sons from his second marriage.

E. Howard Hunt, CIA agent and political warfare operative, was born on October 9, 1918. He died on January 23, 2007, aged 88