Most people can be "placed" – X is "really a Norfolk gentleman"; Y is "a working-class Glaswegian", and so on. Prince Philip evaded such categories.
Was he Greek, German, Danish, British? A plausible case could be made for each of these.
He was born in Corfu, brought up partly in Paris, educated in Germany and Morayshire. To this day, no one in line to the throne may marry a Roman Catholic. It is usually forgotten that the future consort of the Queen was, more exotically, baptised in the Greek Orthodox Church.
Nor was it easy to place Prince Philip in the conventional terms of the British class structure. He was not an aristocrat, or from the county set. Still less was he a plutocrat – when a very young man, he could not afford an overcoat. Since he had only one pair of everyday trousers, he would carefully fold them at night and lay them under his mattress so they were pressed for the morning. His father died penniless; his mother died a nun.
Philip Mountbatten was, by birth as well as marriage, royal. Exasperated by condescending courtiers during his early days at Windsor Castle who said "you will come to love this place, sir", he replied, "my mother was born here, you know". It was true: she was the grand-daughter of Queen Victoria. Fittingly, he died there. Yet because of the traumas of continental Europe in the 20th century, and because his separated parents failed to look after him, the young Philip wandered, almost homeless. Like millions at that time, he was a refugee, if a gilded one.
This unusual background isolated Prince Philip in some ways. It taught him to conceal his sensitivity (he once confided that he did not like going to a concert because "I don't want to be too moved by it"). But it gave him strength when he married into the House of Windsor.
The court, for the most part, did not welcome him. Like, at first, Queen Elizabeth the Queen Mother, it was uneasy about his German connections; but it could not squash him – he was handsome ("We girls were all swooning" one of them, who is still alive, tells me), intelligent, a prince already, and had been a brave sailor who had seen action in the war, emphasising his loyalty to Britain by choosing the Royal Navy over the readily available Greek one.
He was also accomplished: he could fish, shoot, play polo, fly and paint. He could make things with his hands. His inquiring mind made him a keen reader. To use an old-fashioned word, he was always manly.
And although his uncle Lord Mountbatten tried, Philip refused to be enlisted in the court's ancient quarrels and petty intrigues. He looked at it all with the fresh eyes of an outsider.
As one senior royal counsellor puts it, Prince Philip brought "red corpuscules" to the institution of monarchy. Hereditary systems tend to grow weak and inward-looking. Prince Philip was neither: he was mentally and physically tough. If he had not married Princess Elizabeth, he would surely have become an admiral. He wanted things to be shipshape, unfussy, practical, prepared for storms.
His office worked like clock-work. He answered every letter at once. He was decisive, direct, unbedazzled by grandeur, unpompous. He knew the modern world was a hard place for monarchy, but it held no fears for him, and he tried unsentimentally to adapt the institution to the age. He was probably more aware of this need than the Queen herself, who knew no other milieu.
Indeed, he was fascinated by the modern world, and more adventurous than his wife in studying it. Like Victoria's Albert, but with a sense of humour, Prince Philip was keenly interested in what was new. He followed developments in science and technology. He had a feeling for business and was ahead of his time in his interest in the free-market theories of the Institute of Economic Affairs as early as the 1960s.
Before the word "environment" was invented in its modern sense, the Duke of Edinburgh was its advocate, partly through his long presidency of the World Wildlife Fund. Behind the gruff, practical exterior, there was a reflective man.
Prince Philip was interested in religion, and analytical in his approach. In 1966, he founded St George's House, Windsor - the centre for meetings between different faiths and denominations, believers and atheists, clergy and scientists. Such dialogue is taken for granted now, but when it began, it was bold. He published a thoughtful short book of letters exchanged with the Dean of Windsor, in which he sought to reconcile evolution with Christianity.
Without any priggishness, he had a strong moral sense. As a teenager in the mid-1930s, on a school exchange in Germany, he defended a Jewish boy there who was being insulted. Some of his German princely relations were pro-Nazi, but he always made his own views clear.
The young Philip had learnt from Kurt Hahn, his Jewish headmaster at Gordonstoun, the self-reliance which, with his strange and solitary upbringing, he particularly needed. He was made "Guardian" (head boy) of the school and absorbed the idea of leadership as a form of service. This, with its relation to the great outdoors, inspired him to create the vastly successful Duke of Edinburgh's Award Scheme. The phrase "a breath of fresh air" could have been made for Prince Philip, and it sums up his beliefs. He always loved a good practical project. In the 1990s, for instance, he took charge of the enormous task of restoring Windsor Castle after the fire. He loved finding the best craftsmen for the work.
When he married Princess Elizabeth in 1947, Lieutenant Philip Mountbatten did not expect that his wife would soon be on the throne: King George VI was still in his early 50s. With the shockingly early death of the King in 1952, he had to adopt an inevitably subsidiary role much earlier than he had expected. This was not easy for such a man of action and independence, and there were tensions at first. But he had the strength of character not to go on strike.
Sometimes, certainly, he became irritated, but he recognised that his wife's role was of national, Commonwealth, and indeed global importance. He admired the way she carried it out, and did his best to help her. He took a long view, privately remarking 50 years ago, that the Queen was idolised in her youth, was then regarded with less interest in her middle age, but would end up deeply loved when old.
So it has proved. He was also encouraging. With a surprising gallantry which belied his reputation for abruptness, he would often tell the Queen on the way to an official engagement how beautiful she was looking. Theirs was an astonishing partnership – founded on love at first sight in her case, and sustained by deep mutual respect over three quarters of a century.
Although Prince Philip had such a strong personality, and never hesitated to express his views bluntly, he also knew his place. Throughout her nearly 70 years on the throne, the Queen has seen state papers almost every day. Her husband never saw them. He never asked to see them, never tried to guess what was in them, never plotted.
Although keenly interested in politics and public affairs, he never betrayed the slightest ghost of a party preference, never tried to implicate the Queen in any particular opinion, never betrayed her thoughts to the world. He simply gave her his honest view.
In a constitutional monarchy, the mistakes not made are almost as important as the positive things done. It is true that Prince Philip had a reputation for "gaffes". These were politically incorrect, off-the-cuff remarks, often jokes, often misinterpreted by bores or exaggerated by journalists.
They arose from his dislike of small talk and his idiosyncratic humour. But serious mistakes – overstepping his role, seeking to wield power, corruption, failure in duty – of these there were none.
Some criticise him as a father. His daughter, Princess Anne, responded happily to her father's robust and challenging style. For the more sensitive Prince Charles, however, it was harder. With the young Queen so busy with official duties, the main parental decisions were made by Prince Philip. It was he who insisted on sending Charles to Gordonstoun, not Eton.
The regimen did not suit his eldest son. Charles felt that the Gordonstoun idea of a Training Plan against which one daily measured one's fitness - physical, mental and moral - for life, was a permanent exam which he permanently failed. Sensing this, and frustrated by it, Prince Philip could be impatient: he didn't like people being "wet". Some even accused him of belittling the young Charles.
Fundamentally, however, this was unfair. The Duke of Edinburgh loved his eldest son, and gave him the preparation for kingship which Edward VIII had disastrously lacked. He tried hard to be helpful in Prince Charles's marital difficulties. It was not the fault of father or of son that they differed so much in temperament.
Once, I was sitting next to Prince Philip at dinner when he was in his late 70s. The talk turned to retirement. I said I could not imagine him enjoying it, living quietly in the country. His eyes flashed, "I bloody long for it!", he exclaimed. I suddenly saw how much he had given up for the life of what is called "privilege". As a very old man, he led a rural life at Wood Farm, a small, plain, secluded house on the Sandringham estate, driving his coach and four until he was 97.
He liked things simple: "The walls should be white and the ceiling the same colour as the carpet," was his formula.
In their famous prayer, sailors remember "the fleet in which we serve". Such service is arduous, but it comes to an end. Prince Philip's unique service to his adopted country, and to the woman he married, lasted almost until his death.
It was service given – though he would have been embarrassed by the word – lovingly, and for more than twice as long as any other consort of a British monarch. In April 1941, Princess Elizabeth, aged 14, asked a girlfriend, Alathea Fitzalan Howard, "Can you keep a secret?": "Then she said," Alathea recorded in her diary, "that P was her 'boy'…she cuts photos out of the paper!" Eighty years on, she has lost her boy at last, and she, like Victoria, is the widow of Windsor.