Ustinov died of heart failure late on Sunday night in a Swiss clinic at Genolier, near his home in Bursins in vineyards overlooking Lake Geneva.
"He was a great man. He was a human being. He was a unique person, someone you could really count on," said close friend Leon Davico.
Born in London on 16 April 1921, the only son of a Russian artist mother and a journalist father, Ustinov claimed also to have Swiss, Ethiopian, Italian and French blood, everything except English.
His imposing figure was variously described as resembling a teddy bear, a giant panda or a Georgian frontage.
Ustinov was performing by age three, mimicking politicians of the day when his parents invited Ethiopian Emperor Haile Selassie for dinner.
He was educated at the prestigious Westminster School, but hated it and left at 16. He appeared in his first revue and had his first stage play presented in London in 1940, when he was 19.
Ustinov turned producer at 21 when he presented Squaring the Circle shortly before he entered the British army in 1942.
If his plays had a connecting theme, it was a celebration of the little man bucking the system.
One of his most successful was The Love of Four Colonels which ran for two years in London's West End. Davico, who was then starting his career with UNICEF, asked Ustinov to join the UN children's agency as a goodwill ambassador after seeing the play.
'Citizen of the world'
"He was not just a writer and actor. He was someone who really tried to help," Davico said. "He was not only the funniest person I've ever met, but the most intelligent. He was an attentive citizen of the world."
Friends said Ustinov was one of
the funniest people they knew
Ustinov later became a staunch advocate for UNESCO, the United Nations Educational, Scientific and Cultural Organisation. "He never said no to anything UNICEF or the rest of the United Nations asked him to do," said Davico,
Davico said Ustinov recently attended a UNICEF event despite being confined to a wheelchair. Sciatica gave him trouble walking, and diabetes left him with 30% vision and foot problems.
Ustinov's long service as a goodwill ambassador with the United Nations led UN Secretary-General Kofi Annan to joke that Ustinov was the man to take over from him.
In a movie career lasting some 60 years, Ustinov appeared in roles ranging from Emperor Nero to Agatha Christie's Belgian detective Hercule Poirot. He won Academy Awards for supporting actor in the films Spartacus and Topkapi in the 1960s.
More recently he was the voice of Babar the Elephant, played the role of a doctor in the film Lorenzo's Oil, and in 1999 appeared as the Walrus to Pete Postlethwaite's Carpenter in a multimillion-dollar TV movie version of Alice in Wonderland.
No immediate details funeral arrangements were available.