They were such an unlikely match - the corny B movie star whose acting skills made him America's "great communicator", and the earnest leader with little sense of humour.
Yet Ronald Reagan and Margaret Thatcher hit it off in such a big way that she saw Britain's alliance with the US across the Atlantic as being closer than our?relationship?with France just across the Channel.
She believed America's military might kept the world stable but, even more fundamentally, she believed in the effectiveness of American-style capitalism. She had a cordial?relationship?with President Reagan's Democrat predecessor, Jimmy Carter, but she despised what she saw as his wishy-washy liberalism.
Reagan's politics suited her better. They were both dogmatic in their hard-line monetarist policies and each were deeply distrustful of a perceived expansion of communism. But, more importantly, the man suited her better.
There was a clear chemistry. He was gallant towards her, and she loved tall, older men, especially those such as Reagan who had film-star good looks.
Reagan was out of his depth with world statesmen so was grateful for an ally, especially one who spoke English.
They formed a mutual admiration that transcended politics and lasted to the end of his life.
But they could hardly have been more different. Reagan was a lazy, optimistic broad-stroke politician, more than happy to delegate. Thatcher was a workaholic who thought nobody but she could do a job well, with a grasp of detail that made her formidable as an opponent.
She knew his faults. "Not much grey matter, is there?" she once said, privately.
But in public she deferred to him, almost girlishly. She first met him when he was Governor of California, and she was not yet in office.
They were both delighted when the other landed the top job and she was the first foreign visitor to the White House after his inauguration in 1981.
It was at the G7 summit that tear they really became close, dropping the formal address in their letters and becoming Dear Margaret and Dear Ron.
His staff realised her worth as she helped him navigate tricky diplomatic waters and, at times, she presented US policy better than he did on the world stage.
They became a very powerful double act.
When he was in trouble domestically over allegations that America exchanged arms for the release of Iranian hostages she leapt to his defence.
She went on US American television saying how much she trusted him. And their?relationship?was cemented by the threat from Russia.
The world was in the depths of the Cold War and the threat of nuclear annihilation was very far away.
In Britain, the procurement of Trident weapons and the siting of cruise missiles at Greenham Common brought the issue of nuclear proliferation to the fore.
The American airbase in Berkshire became the focus of one of the longest campaigns as a peace camp was set up outside to protest against the Government's decision.
The publication in 1980 of Protect and Survive, the Government's guide to living through a nuclear war, added to the fear.
The introduction of the Star Wars shield - more formally known as the Strategic Defence Initiative - which aimed to shoot down incoming nuclear missiles, was widely derided and only served to increase East-West tensions.
But the arrival of Mikhail Gorbachev as chairman of the Supreme Soviet saw a thaw in international relations.
Thatcher first met him in 1984 when he visited Britain. He was a member of the Politburo and visited Chequers for lunch.
The diametrically opposed political opponents found common ground and Thatcher famously said: "I like Mr Gorbachev, we can do business together."
Thatcher lavished high praise on her US ally at the end of the Cold War.
She said: "Ronald Reagan had a higher claim than any other leader to have won the Cold War for liberty and he did it without a shot being fired."
He later responded: "This great lady has not only served her country well, she has served the free world well. She is truly a great statesman. So much so that I'll correct what I just said: She is a great stateswoman holding her own among all the statesmen of the world."
There were political hiccups along the way. Thatcher was desperate for America's support during the Falklands, something initially refused by the US.
Records recently released show underlying tensions between the two leaders as Reagan advocated talks before invasion.
In one transatlantic conversation between the pair Thatcher told him she, "was sure that the president would act in the same way if Alaska had been similarly threatened... self-determination for the islanders had to be the paramount consideration."
There were also tensions over American sanctions against Russia, the US investigation into British Airways which held up her privatisation plans, and the invasion of Grenada, a Commonwealth member.
Thatcher was also determined that history would see her as America's ally, not its poodle. Despite this, she agreed to allow American bombers to fly from British bases to bomb Libya, especially after the shooting of WPC Yvonne Fletcher in 1984 and Libya's secret arming of the IRA.
It caused her big problems at home but she weathered the storm, and felt it was more than justified to keep her close?relationship?with the US.
On a personal level, the Reagans and the Thatchers got on well.
They were relaxed together, they enjoyed each other's company. When they were together in private, they could talk freely and frankly, as old friends.
After they had both left office, they kept in touch.
Reagan suffered from Alzheimer's disease, and throughout Thatcher kept in touch with his wife Nancy. He died of pneumonia in California in 2004.
Thatcher never achieved a closeness like this with any other world leader.
Now read about her struggles at home with the IRA.