To those not in the know, he would introduce himself as Robert Hunter. An Australian retiree, he said, whiling away his latter years with his notably younger Cuban wife, in a simple bungalow overlooking the Playas del Este, a string of white sand beaches outside Havana.

The cover fooled most visitors. But there were plenty of clues it wasn’t true. The broad Brooklyn accent; the Hemingwayesque white beard. And a disarming, encyclopaedic knowledge of African and Middle Eastern political leaders, covering five decades.

Robert Hunt wasn’t really Robert Hunt at all. He was Frank Terpil, rogue CIA agent. A man described as a “maniac” by the undercover US policeman who helped convict him in New York in 1981 on charges of seeking to sell 10,000 machine-guns and 20 tonnes of plastic explosives to Libya. A coldly intelligent, no-scruples dealmaker, and confidant of the later 20th century’s most brutal dictators, from the Shah of Iran to Idi Amin.

After a few shots of rum, he would let his guard down. Inside his hilltop Cuban home, shaded by tropical trees, Frank (he reverted to his real name in private, in his last months) took pleasure in recounting, with not the slightest indication of remorse, chilling tales of how he helped “facilitate” the world’s maverick regimes.

Whether the requirement was poison, weapons or mercenaries, he was the man to call. “It was commercial. And neutral,” he always said.

Terpil was born in Brooklyn, New York, in 1939. His father, who worked for a local telecoms company, died when his only son was 12. After a short spell in the US army, he joined the CIA in 1965. His first job was with what was known as the Technical Services division, that part of the agency that specialised in adapting technology and weaponry for covert work.

In 1970 Terpil was posted to India. He soon showed signs of a taste for the good life, buying himself a Cadillac, renting a large house in the desirable Anand Niketan area of New Delhi, and developing a taste for gin and lime. To pay for it all, he needed to supplement his modest federal salary.

He found a simple solution. Banks in neighbouring Afghanistan were mistakenly overvaluing the Indian rupee. Terpil would ship planeloads of hard currency to Kabul, change them into rupees, then re-exchange them, at a vast profit, back in Delhi. “It was so easy,” he said. His bosses at the CIA were, officially at least, unimpressed. Terpil was asked to leave the agency in 1971. He says that he went “freelance”. Just how freelance is a secret he has taken to his grave. There is evidence that the CIA never quite let him go.

After India, Terpil sought opportunities in the Middle East, specifically Libya. In 1973 Muammar Gaddafi had declared a popular revolution, promising to rid Libya of “poisonous” foreign influence. He also needed weapons to destroy his opposition.

Terpil, who said he first met Gaddafi in the Libyan embassy in London in the mid-1970s, offered his services. He would ship arms and source the gadgets, including exploding briefcases and ashtrays, to deploy against the leader’s enemies. He also says he helped provide mercenaries for “anti-terrorist operations”. The mercenaries were mostly American.

Alongside Gaddafi, Terpil went on to do business in the late 1970s with the Ugandan dictator Idi Amin, who was by then struggling to maintain his vicious grip on power amid widespread dissent. Amin gave his American friend the affectionate nickname Waraki or “white lightning”.

During an interview broadcast in the 1982 documentary, Confessions of a Dangerous Man, the former CIA agent admitted having a permanent office in the “State Researches Institution” in Kampala. Amin’s enemies are known to have been tortured in the basement. Terpil claimed he was not fully aware of what was going on. “It was a domestic issue,” he later said in Havana.

The night Amin’s rule finally ended, on 13 April 1979, Terpil was on the presidential plane to Libya. He recalls loading steel trunk-loads of gold on to the aircraft, just before they flew out from Entebbe.