Tony Mendez was a CIA surveillance specialist. So how did he prepare for his role as an Irish film-maker in the mission to free hostages in Tehran that is dramatised in Ben Affleck's Oscar-nominated 'Argo'? "I drank a lot of pints"

For almost two decades Antonio Mendez, a retired CIA agent, couldn't talk about his leading role in one of the US spy agency's most audacious covert rescues: the exfiltration of six US diplomats from Tehran in November 1979, during the Iranian hostage crisis.

Tony Mendez is clearly enjoying the attention the daring operation is now getting through its depiction in Ben Affleck's film Argo, a best-picture nominee at this weekend's Academy Awards ceremony, in Los Angeles.

A 25-year CIA veteran, Mendez, who is of Irish, Italian and Mexican ancestry, managed the "Canadian caper", in which he posed as an Irish film-maker, whom he named Kevin Costa Harkins, and the six US diplomats posed as a Canadian film crew scouting Tehran for locations for a fake Hollywood movie that they called Argo.

The six had escaped the US embassy in the Iranian capital after it was overrun by militant students. They hid in the Canadian embassy before Mendez led them out of the country with fake Canadian passports.

The CIA's role in the operation remained a secret until President Bill Clinton declassified the operation, in 1997. Mendez was decorated with an Intelligence Star, an agency medal, for his role.

Mendez worked as an artist before joining the CIA, in 1965. At the agency he was based in South and Southeast Asia and the Middle East, forging official records and creating disguises to protect field agents. The CIA's Office of Technical Service was the agency's most creative division, the part of the organisation that wired cats with microphones for eavesdropping and planted explosives in Fidel Castro's cigars. "If I were able to tell you how highly skilled we were, you wouldn't believe it," he says.

In one famous disguise that Mendez created during the Vietnam War, using the expertise of the Hollywood make-up artist John Chambers, the CIA transformed a black CIA officer and an Asian diplomat into two white businessmen in Laos, a neutral but politically key country that Mendez says was saturated with intelligence officers.

"There were all sorts of spies in the diplomatic capital of Laos, and they were all trying to meet their sources so they could get the minutes of these cabinet meetings, high-level policymaking intelligence - it got very crowded," he says.

"The intelligence officers would go into town and try to meet their foreign agents and pick them up with a car. We called it a pick-up, where someone jumps into a rolling car and away you go, hoping nobody saw you or who you were meeting. It was a like a fish bowl - all sorts of fish swimming around."

The CIA's African-American case officer would have stood out in Laos. The disguise was good enough to fool a group of armed soldiers at a roadblock who stopped the agent and his source, and its success prompted the start of a programme of transforming agents' identities so they could work in hostile areas.

"If you were to ask me was it as good as Tom Cruise" - in the Mission: Impossible movies - "I would say every bit. But Tom Cruise requires about five hours to get ready. We had to do it in five seconds, with no retakes."

The former CIA technical officer estimates that the one meeting in Laos saved the United States $4 billion. About 85 per cent of the key intelligence questions the CIA raised about the Soviet Union and its weapons development were answered in South Asia as a result of the agency's work there, he says, as the Soviets sold their weapons to communist governments in the region. "We were mining high-grade ore."

For his CIA job Mendez needed skills similar to those of a creative artist working in Hollywood, but he never considered leaving the agency - and pretending to be a film producer didn't whet his appetite to work in movies, either. "I was having too much fun," he says.

To create foolproof disguises, Mendez says you need basic hand skills and a knowledge of chemistry. "You have to have to a thirst for knowledge about the world, because what you are doing as a master of disguise is creating scenarios around the world that allow you to come and go, and not compromise your assets. So hand skills, the ability to travel, observe and create things are necessary," he says. "You also have to be a romantic, because you can't tell anybody what you have done, so you have to get your approval from within."

Mendez says that recognising new threats is always a problem for intelligence services. The Iranian hostage crisis showed that the "rules of engagement were different". "There were no rules, in fact, only a vicious, rabid contingent of people who were unpredictable: they are not going to the negotiating table; they are going to blow up the table."

For the Iranian exfiltration, Mendez says he chose the guise of an Irish film producer because the Irish blend in. He also has Irish blood in him from his roots in Nevada, so this seemed a perfect alter ego.

"As you know, the Irish are ubiquitous around the world. What you want to do is use some cover legend that puts you in a large population so you can blend in. The Irish are nonthreatening," he says. "The Irish are sort of charming, you know - you want to be a friendly face. They are always ready to tell you a good story, and we made up some good stories."

During the fake film-scouting mission to Tehran, locals were more interested in his Hollywood connections than in his Irish identity, despite a well-practised Irish accent, which he says was "a bit of all right".

"I have been working on it for years - that is why I hang out in pubs. I listened to very many recordings. I drank a lot of pints of Guinness."