The Stanford Dictionary of Philosophy defines friendship as ‘a distinctively personal relationship that is grounded in a concern on the part of each friend for the welfare of the other, for the other’s sake, and that involves some degree of intimacy’. In Nicomachean Ethics, Book VIII, Aristotle talks of three distinguishing three kinds of friendship: friendships of pleasure, of utility, and of virtue. In modern times, friendship is often categorised as acquaintances, social friends, intimate friends, the epitome of friends. And, of course, BFFs.

On International Day of Friendship, let’s look at history’s best BFFs.

Frank Sinatra & John F Kennedy

He was the flamboyant President of the United States of America, he, the singer with a dulcet voice and a huge fan base. And the two were great friends. John F Kennedy (1917-1963) and Frank Sinatra (1915-1998) were great friends and the joke was that Kennedy wanted to be Sinatra and Sinatra wanted to be Kennedy, as mentioned in Steven Watts’ JFK and the Masculine Mystique: Sex and Power on the New Frontier. “We’re indebted to a great friend — Frank Sinatra,” Kennedy had said on the night before his inauguration as the US President. It was Sinatra who introduced Kennedy to Marilyn Monroe and also labelled the room in his house where Kennedy had slept with a sign that read ‘JFK Slept Here’. The friendship did not last long but Sinatra is said to have cried for days after JFK was assassinated.

Queen Victoria & Abdul Karim

Abdul Karim came as a ‘gift from India’ in 1887 when Queen Victoria hosted a lavish banquet for foreign royalty and dignitaries to celebrate 50 years on the throne. The Queen and her servant developed a friendship that scandalised a prudish nation. Karim was the queen’s beloved munshi, who taught her Urdu, educated her on Indian affairs, and introduced her to curry. The Queen showered him with gifts, titles and honours that infuriated the royal family members. In her diary, the Queen mentions her first impression of Karim as ‘tall man with a fine serious countenance’ and in her final wishes, she wanted Karim to be one of the principal mourners at her funeral, an honour reserved only for the monarch’s closest friends and family.

Ravi Shankar & George Harrison

“The friendship with George started in 1966 and that’s when I met him along with the other three, but George was something very special from the very beginning. Something clicked between us…” Sitarist Pandit Ravi Shankar (1920-2012) wrote about George Harrison (1943-2001), one of the founder members of The Beatles. “I remember thinking I’d like to meet somebody who will really impress me. And that’s when I met Ravi, which was funny, because he’s this little fellow with an obscure instrument from our point of view, and yet it led me into such depths” wrote George Harrison. This personal and musical friendship lent a huge impact on music in the late 1960s; the two also organised the famed Concert for Bangladesh in 1971.

Thomas Edison & Henry Ford

Henry Ford (1863-1947) attended the 1896 convention of the Association of Edison Illuminating Companies, held at the Oriental Hotel on Manhattan Beach in Brooklyn, New York. During a banquet, Ford met his boyhood hero, Thomas Edison (1847-1931) and became lifelong friends. Edison and Ford owned vacation homes near one another in Fort Myers, Florida, and calling themselves the Vagabonds, Edison and Ford, along with Harvey Firestone, and naturalist John Burroughs, took annual camping trips between 1916 and 1924. When Ford introduced the Model A, his first all-new car in 19 years, he gave the first example to Thomas Edison. When Edison became wheelchair-bound, Ford bought his own wheelchair so he could commiserate with (and race) with his friend.

Catherine the Great & Voltaire

In 2006, at a Sotheby's auction in Paris, 26 handwritten letters were sold for staggering £400,000 setting a new record price for 18th-century correspondence. But these were no ordinary letters - the correspondence was between Catherine the Great, Russia's most famous female ruler, and Voltaire, one of France's pre-eminent Enlightenment philosophers. They never met but corresponded for 15 years until Voltaire's death. Voltaire called Catherine ‘The Star of the North’ and was happy to be her ally in what both regarded as feudal backwardness.

Harry Houdini & Sir Arthur Conan Doyle

In 1920, two great men met - one who created the unforgettable Sherlock Holmes, and the other an illusionist and escapologist, the highest paid entertainer of his time. Sir Arthur Conan Doyle (1859-1930) and Harry Houdini (1874-1926) bonded over a shared interest in spiritualism - after the death of his son, Doyle became a devout believer in life after death while Houdini yearned that he might be able to communicate with his dead mother. Their friendship - and a bitter rift later - is immortalised in the 2016 British TV mini-series Houdini & Doyle.

Mark Twain & Nikola Tesla

Much before he met Samuel Clemens (Mark Twain, 1835-1910), inventor Nikola Tesla (1856-1943) had read his books - as a child he had struggled with illnesses and on sick days he found comfort in Twain’s stories. Twain was curious about inventions, the two met in early 1800s and became friends. Twain often got involved with some of Tesla’s experiments (he invented the Tesla coil and alternating-current (AC) electricity) and appeared in photographs taken in his New York laboratory.

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