One day Andrew Vicari was sketching King Khalid of the Saudi Royal Family. “The King, a fantastically handsome and most amiable man, was sitting at the end of the room,” he recalls. “But the chief of protocol would get upset with me when I addressed the King directly. When I asked the King to please lift his hand a little higher, the chief of protocol stepped in and said: ‘Please, address your remarks to me, not to His Majesty’.”

Such are the travails of the court painter to the Saudi Royal Family. The Welsh-born Vicari is both influential and wealthy, with a fortune estimated at £92 million, though his work is better known in the Middle East than here.

“Goya, van Dyck and Holbein were all court painters, and so I am just following in a great tradition,” he says. “Some people sneer at the thought of court painter, I don’t know why. It’s a great privilege. Some of the best paintings in the world were done of kings and princes.”

Vicari is currently in the United Arab Emirates to launch the Dubai Community Theatre and Arts Centre with an exhibition of portraits of “50 iconic figures of the 20th century” painted by himself and including Augustus John, Pablo Picasso and Henri Matisse.

Of Italian ancestry, Vicari was born in Port Talbot in 1938 and moved to Neath as a child. “I was 14 when my grammar-school teacher entered my art in the National Eisteddfod of Wales. I was in Italy on holiday when my father sent a telegram saying: ‘You’ve won £10 and a medal. I’m keeping the money because I’ve supported you long enough, but you can have the medal’.” Vicari knew “the artist’s life [was] for me, doing something so easy and getting paid for it”.

The young Vicari was inspired by a Polish refugee painter living in Neath. On Saturdays he would visit the artist and watch him paint. Equally influential were the poets Walt Whitman and William Blake and the painters Tintoretto and Raphael.

He is less impressed by today’s names: Hockney he feels is “dreary”, and don’t mention Tracey Emin, whom he refers to as the “knickers lady”, and Damien Hurst, “the taxidermist who pickles fish”.

Vicari attended the Slade — “I was the youngest student ever admitted” — and his professors and supporters included Lucian Freud, Josef Herman, Augustus John, Sir William Coldstream and Francis Bacon. His models have been the rich and powerful, including his favourite model, Princess Caroline of Monaco, whom he describes as “one of the world’s great misunderstood beauties and one of the most literate people I have met”.

Vicari first went to Saudi Arabia in the early 1970s. “My first meeting was with the Minister of Finance, Sheikh Mohammed Abu Khail, who admired my work. He said: ‘We’d like you to paint 60 paintings to decorate the King Faisal Conference Centre’.” It was a great success and led to commissions to paint portraits of the late King Khalid and, later, King Fahd.

“At first I was given photographs to paint from, but I said no. So they arranged for me to wait in a hall outside a conference room and when King Khaled came out I had to sketch him. Walking backwards, pencil in one hand and pad in the other, I frantically sketched him before he reached the end of the hallway. Eventually he came around and agreed to pose for me.”

His largest work consists of 225 oil paintings depicting battle scenes and portraits of world leaders, called From War to Peace in the Gulf: The Liberation of Kuwait. Armed only with a paintbrush, Vicari joined the battle front to depict scenes of the 1991 Gulf War for posterity and was later described as the only official artist of the war.

Prince Khalid bought 125 of the massive oil paintings for $24 million (£13 million). General “Stormin’ ” Norman Schwarzkopf was the last person to sit for him during the Gulf War. Vicari says: “He was so pleased with his portrait, he presented me with his khaki cap, which I now wear while painting.”

Vicari’s latest commission, worth $25 million, will be a family portrait measuring 30m by 9m (100ft by 30ft), larger than a tennis court. He is cautious about disclosing too much information, but the painting will be called The Parable of Majesty, the most expensive artwork of its kind.

Vicari has become good friends with the Saudi royals and they have given dinners for him. The Deputy Governor of Riyadh once introduced him to “the largest person I have ever met — when I put my hand into his it disappeared. It turned out he was a hangman. He was a hell of a nice guy, even though once a week he executed about five people.”