Ustinov, a renaissance man whose talents included writing plays, movies and novels as well as directing operas, also devoted himself to the world's children for more 30 years as a goodwill ambassador for UNICEF.
He died of heart failure late Sunday night in a Genolier clinic near his home at Bursins in Swiss vineyards overlooking Lake Geneva, close friend Leon Davico, a former UNICEF spokesman, told The Associated Press.
"He was a great man. He was a human being. He was a unique person, someone you could really count on," said Davico.
"He was a giver, throughout everything, and a warm, wonderful human being," said his manager, Steve Kennis, who added Ustinov always saw the bright side of everything.
Born in London on April 16, 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. He was proud of his Russian heritage, said Kennis.
Ustinov made some 90 movies and also wrote books and plays. He directed films, plays and operas. His narration of Tchaikovsky's "Peter and the Wolf" won him a Grammy. He was nominated for an Oscar for his screenplay of 1968's "Hot Millions."
Among his film roles were a nomad in the outback who befriends a family in "The Sundowners," a one-eyed slave in "The Egyptian," Agatha Christie's Belgian detective Hercule Poirot in "Death on the Nile," and Abdi Aga, an illiterate tyrant with pretensions of learning in "Memed My Hawk."
Ustinov won best supporting actor Oscars for the role of Batiatus, owner of the gladiator school in "Spartacus" (1960), and as Arthur Simpson, an English small-time black marketeer in Turkey who gets caught up in a jewel heist, in "Topkapi" (1965).
His Nero — the Roman emperor who presided over the throwing of Christians to the lions — won him a Golden Globe for best supporting actor in the 1951 movie "Quo Vadis." He was also nominated for an Academy Award for that role.
He also won three television Emmys, portraying the English lexicographer Samuel Johnson in "Dr. Johnson" and as Socrates in "Barefoot in Athens." In "A Storm in Summer," his Emmy came for playing an aged Jewish delicatessen owner in Long Island at grips with racial prejudice in the shape of a proud black youth.
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.
Writing was what he enjoyed most, said biographer John Miller. If his plays had a continuing 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 starting his career with UNICEF, asked Ustinov to join the U.N. children's agency as a goodwill ambassador after seeing the play.
Ustinov later became a staunch advocate for UNESCO, the United Nations Educational, Scientific and Cultural Organization. "He never said no to anything UNICEF or the rest of United Nations asked him to do," said Davico.
Davico said Ustinov recently attended a UNICEF event despite needing a wheelchair — sciatica gave him trouble walking, and diabetes left him with 30 percent vision and foot problems.
He later 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. When I was young, I was brought up in an atmosphere which was just loaded with prejudices," he said in 2001.
Michael Winner, who directed Ustinov as Hercule Poirot in the 1988 movie "Appointment With Death," described the actor as a "marvelous man, a great wit, a great raconteur, a man of the world."
"He was a very good actor but he wasn't used as an actor as much as he should have been because he became famous as Peter Ustinov," Winner told The Associated Press in a telephone interview.
Ustinov treated getting older the way he treated everything else in his life — as another experience to be added to his repertoire of anecdotes, quips and material for books.
When he turned 60 in 1981, Ustinov was asked if he was tempted to take things a little easier. "I only feel 59," he said.
"But what really surprises me," he added, "is that I don't say many different things now than I did when I was 20. The only difference is that having white hair means that people tend to listen now while they never did before."
Asked what he wanted on his tombstone, Ustinov replied "Keep off the grass," reports CBS News Correspondent Steve Holt.
When he was knighted by the Queen of England in 1990, his main worry was how to reply to the invitation from Buckingham Palace.
"The invitation said, 'Delete whichever is inapplicable: I can kneel — I cannot kneel.' But there was nothing for those who can kneel but not get up," Ustinov recalled.
But he remained active until close to his death, playing himself in the 2003 TV movie "Winter Solstice."
Ustinov was married three times, and is survived by his four children and his third wife.