A tireless advocate of the rights of children worldwide

Although Peter Ustinov was known globally as an engaging actor, mimic and wit, he had a strong moral centre to his beliefs and was a lifelong campaigner against prejudice and insularity.

He set up a foundation dedicated to understanding between people across the globe and between generations.

"I think knowing people is the best way of getting rid of prejudices," he said in 2001. "When I was young, I was brought up in an atmosphere which was just loaded with prejudices. When I came into my first classroom at the age of six there was a large oleograph of Jesus Christ holding a boy scout by the hand and pointing out the extent of the British Empire on the map. As a small foreign boy I was outraged by this."

For 35 years, he was a goodwill ambassador for Unicef, the United Nations' children's rights organisation. Among the tributes to him yesterday, one from Mr Kofi Annan, the general secretary of the UN, would likely have given him much satisfaction.

"Sir Peter's exceptional wit, intelligence and creativity were fully matched by his compassion, conscience and character. Not only did his talents bring joy to millions of people, he served Unicef with dedication and distinction for more than three decades to bring attention to the needs of children everywhere."

Unicef's executive director, Carol Bellamy, said: "The children of the world have lost a true friend in Sir Peter Ustinov. Sir Peter had a magical way with children and an inimitable way of making their problems matter to people all over the world."

Unicef said that if Sir Peter couldn't speak directly to children, despite his linguistic prowess, he would make them laugh any way he could, even if it meant - and it often did - "getting down on all fours and making uncannily lifelike animal noises".

Sir Peter didn't visit children to observe them, but to engage them. He played ping-pong with children in Egypt, rode bicycles with them in Kenya, vaccinated them in China, and danced with them in Cambodia and Thailand, said the organisation.

"Sir Peter never lost his belief that the world could change, and that even children living in the most heartbreaking conditions could see a better future," Bellamy said. "We will miss him terribly, but will keep his memory alive the best way we know - by emulating his unwavering commitment to give children everywhere the life they deserve."

A friend Leon Davico, a former Unicef spokesman and the man who first involved him in the organisation, described him yesterday as "someone you could really count on".

"He was a great man. He was a human being. He was a unique person ... He was not just a writer and actor. He was someone who really tried to help. He was not only the funniest person I've ever met, but the most intelligent. He was an attentive citizen of the world," said Mr Davico.