Prince Philip, the Duke of Edinburgh, has stood at the Queen's side for nearly 60 years. He is recognised the world over and has become the longest serving consort in British history. But he has told the BBC that he had to work out for himself what his role was "by trial and error".
"There was no precedent. If I asked somebody, 'What do you expect me to do?' they all looked blank. They had no idea, nobody had much idea."
Over the years, the duke has involved himself with more than 800 different organisations.
But he was very reluctant to talk about himself and his achievements to Fiona Bruce in a special BBC One programme to mark his 90th birthday and refused to say what he was most proud of.
"I couldn't care less," he said when asked if he thought he had been successful in his role. "Who cares what I think about it, I mean it's ridiculous."
One of Prince Philip's most successful initiatives has been to create The Duke of Edinburgh's Award, which has stretched the capabilities of more than seven million young people globally since 1956.
But he said he could not take credit for the highly successful scheme. "I don't run it - I've said it's all fairly secondhand the whole business. I mean, I eventually got landed with the responsibility or the credit for it.
"I've got no reason to be proud of it. It's satisfying that we've set up a formula that works - that's it."
The duke was also a champion of the early environmental movement and was the first president of the World Wildlife Fund. He was more happy to open up about his passion for conservation.
"If we've got this extraordinary diversity on this globe it seems awfully silly for us to destroy it. All these other creatures have an equal right to exist here, we have no prior rights to the Earth than anybody else and if they're here let's give them a chance to survive."
But he said he would not describe himself as green: "I think that there's a difference between being concerned for the conservation of nature and being a bunny hugger... people who simply love animals.
"People can't get their heads round the idea of a species surviving, you know, they're more concerned about how you treat a donkey in Sicily or something."
He said he believed the growing human population was the biggest challenge to conservation and "voluntary family limitation" was the only way to tackle it.
The duke's comments on the environment reflect his reputation for plain speaking.
"He always speaks his mind, sometimes not necessarily with a high degree of tact," says his cousin Countess Mountbatten.
"But on the other hand, I think that people have come to expect that of him, and they really rather enjoy it and they think, how nice to hear somebody actually say what they think."
For decades the duke has made off-the-cuff remarks that have been reported around the world.
On a tour to China, he quipped to British students, off the record, that if they stayed in China much longer they would come back with slitty eyes.
When Fiona Bruce suggested that some people may have thought he should not have said that, he replied: "It has no effect in China if that's what you're worried about."
Pushed on what he felt about the comment, he admitted: "I'd forgotten about it."
So does he feel the press has been unfair to him or misrepresented him?
"I suppose, yes, occasionally but I think it has its own agenda and, and that's it, you just have to live with it."
Prince Philip admitted he did not want to be interviewed by the BBC for a documentary to commemorate his 90th birthday and Fiona Bruce's attempts to delve into his early years were given short shrift.
As a member of the exiled Greek royal family he had a nomadic childhood living in France, England and Germany. Asked if that was unsettling, he replied: "Well I just lived my life - I haven't been trying to psychoanalyse myself all the time."
Aged just 10, Prince Philip was separated from every member of his immediate family, as they moved to live in different countries. But he said that was "no great deal".
His reluctance to speak about all aspects of his life is due to modesty, according to his son, Prince Edward.
"My father plain and simply is very modest about himself and doesn't believe in talking about himself. One of his best pieces of advice he gives to everybody is talk about everything else, don't talk about yourself - nobody's interested in you."
At 90, Prince Philip said he was "winding down" his involvement with charities.
"I reckon I've done my bit so I want to enjoy myself a bit now, with less responsibility, less frantic rushing about, less preparation, less trying to think of something to say. On top of that your memory's going, I can't remember names and things," he admitted.
"It's better to get out before you reach the sell-by date."