Sir Peter Alexander Ustinov, CBE, FRSA (born Peter Alexander von Ustinov; /ˈjuːstɪnɒf/ or /ˈuːstɪnɒf/; 16 April 1921 – 28 March 2004) was an English actor, Writer, dramatist, filmmaker, theatre and opera Director, stage designer, Screenwriter, Comedian, humorist, newspaper and magazine columnist, radio broadcaster, and television presenter. He was a fixture on television talk shows and lecture circuits for much of his career. An intellectual and diplomat, he held various academic posts and served as a Goodwill Ambassador for UNICEF and President of the World Federalist Movement.

Jona (or Iona) worked as a press officer at the German Embassy in London in the 1930s, and was a reporter for a German news agency. In 1935, two years after Adolf Hitler came to power in Germany, Jona von Ustinov began working for the British intelligence Service MI5 and became a British citizen, thus avoiding internment during the war. He was the controller of Wolfgang Gans zu Putlitz, an MI5 spy in the German embassy in London who furnished information on Hitler's intentions before the Second World War. (Peter Wright mentions in his book Spycatcher that Jona was possibly the spy known as U35; Ustinov says in his autobiography that his father hosted secret meetings of senior British and German officials at their London home.) Ustinov's great-grandfather Moritz Hall, a Jewish refugee from Kraków and later a Christian convert and collaborator of Swiss and German missionaries in Ethiopia, married into a German-Ethiopian family.

In 1939, he appeared in White Cargo at the Aylesbury Rep, where he performed in a different accent every night.

Ustinov was the winner of numerous awards over his life, including two Academy Awards for Best Supporting Actor, Emmy Awards, Golden Globes and BAFTA Awards for acting, and a Grammy Award for best recording for children, as well as the recipient of governmental honours from, amongst others, the United Kingdom, France, and Germany. He displayed a unique cultural versatility that has frequently earned him the accolade of a Renaissance man. Miklós Rózsa, Composer of the music for Quo Vadis and of numerous concert works, dedicated his String Quartet No. 1, Op. 22 (1950) to Ustinov.

After the war, he began writing; his first major success was with the play The Love of Four Colonels (1951). He starred with Humphrey Bogart and Aldo Ray in We're No Angels (1955). His career as a dramatist continued, his best-known play being Romanoff and Juliet (1956). His film roles include Roman Emperor Nero in Quo Vadis (1951), Lentulus Batiatus in Spartacus (1960), Captain Vere in Billy Budd (1962), and an old man surviving a totalitarian Future in Logan's Run (1976). Ustinov voiced the anthropomorphic lions Prince John and King Richard in the 1973 Disney animated film Robin Hood. He also worked on several films as Writer and occasionally Director, including The Way Ahead (1944), School for Secrets (1946), Hot Millions (1968), and Memed, My Hawk (1984).

Between 1952 and 1955, he starred with Peter Jones in the BBC radio comedy In All Directions. The series featured Ustinov and Jones as themselves in a London car journey perpetually searching for Copthorne Avenue. The comedy derived from the characters they met, whom they often also portrayed. The show was unusual for the time, as it was improvised rather than scripted. Ustinov and Jones improvised on a tape, which was difficult, and then edited for broadcast by Frank Muir and Denis Norden, who also sometimes took part.

In the 1960s, he became a Swiss resident to avoid the British tax system of the time, which heavily taxed the earnings of the wealthy. However, he was knighted in 1990 and was appointed chancellor of Durham University in 1992, having previously been elected as the first rector of the University of Dundee in 1968 (a role in which he moved from being merely a figurehead to taking on a political role, negotiating with militant students). Ustinov was re-elected to the post for a second three-year term in 1971, narrowly beating Michael Parkinson after a disputed recount.

He was the subject of This Is Your Life on two occasions: in November 1977 when he was surprised by Eamonn Andrews at Pinewood Studios on the set of Death on the Nile, and a week before, he was surprised at a book signing at book printers Butler and Tanner in Frome, Somerset. This footage was not used, as Ustinov flatly refused to take part and swore at Andrews. His wife persuaded him to change his mind. He was surprised again in December 1994, when Michael Aspel approached him at the United Nations headquarters in Geneva.

In half a dozen films, he played Agatha Christie's detective Hercule Poirot, first in Death on the Nile (1978) and then in 1982's Evil Under the Sun, 1985's Thirteen at Dinner (TV movie), 1986's Dead Man's Folly (TV movie), 1986's Murder in Three Acts (TV movie), and 1988's Appointment with Death.

His autobiography, Dear Me (1977), was well received and had him describe his life (ostensibly his childhood) while being interrogated by his own ego, with forays into philosophy, theatre, fame, and self-realisation. In the later part of his life (from 1969 until his death), his acting and writing tasks took second place to his work on behalf of UNICEF, for which he was a Goodwill Ambassador and fundraiser. In this role, he visited some of the neediest children and made use of his ability to make people laugh, including many of the world's most disadvantaged children. "Sir Peter could make anyone laugh," UNICEF Executive Director Carol Bellamy is quoted as saying. On 31 October 1984, Ustinov was due to interview Prime Minister of India Indira Gandhi for Irish television. She was assassinated on her way to the meeting.

Ustinov also presented and narrated the official video review of the 1987 Formula One season, and narrated the documentary series Wings of the Red Star. In 1988, he hosted a live television broadcast entitled The Secret Identity of Jack the Ripper.

Ustinov was the President of the World Federalist Movement from 1991 to 2004, the time of his death. WFM is a global NGO that promotes the concept of global democratic institutions. WFM lobbies those in powerful positions to establish a unified human government based on democracy and civil society. The United Nations and other world agencies would become the institutions of a World Federation. The UN would be the federal government and nation states would become similar to provinces.

In 1997 singer-songwriter Lauren Christy released a song entitled "The Night I Saved Peter Ustinov", on her album Breed. In it Christy recounts a story in which she saves Ustinov from a suicide attempt. In Knowing Me Knowing You, when asked who the most famous Philosopher alive is, after much consternation, Alan Partridge replies "Peter Ustinov".

Ustinov was a frequent defender of the Chinese government, stating in an address to Durham University in 2000, "People are annoyed with the Chinese for not respecting more human rights. But with a population that size it's very difficult to have the same attitude to human rights." In 2003, Durham's postgraduate college (previously known as the Graduate Society) was renamed Ustinov College.

Ustinov went to Berlin on a UNICEF mission in 2002 to visit the circle of United Buddy Bears that promote a more peaceful world between nations, cultures, and religions for the first time. He was determined to ensure that Iraq would also be represented in this circle of about 140 countries.

In 2003, Durham University changed the name of its Graduate Society to Ustinov College in honour of the significant contributions Ustinov had made as chancellor of the university from 1992 until his death.

Ustinov died on 28 March 2004 of heart failure in a clinic in Genolier, near his home in Bursins, Vaud, Switzerland. He was so well regarded as a goodwill ambassador that UNICEF Executive Director Carol Bellamy spoke at his funeral and represented United Nations Secretary-General Kofi Annan.

Ustinov was married three times—first to Isolde Denham (1920–1987), daughter of Reginald Denham and Moyna Macgill. The marriage lasted from 1940 to their divorce in 1950, and they had one child, daughter Tamara Ustinov. Isolde was the half-sister of Angela Lansbury, who appeared with Ustinov in Death on the Nile. His second marriage was to Suzanne Cloutier, which lasted from 1954 to their divorce in 1971. They had three children, two daughters, Pavla Ustinov and Andrea Ustinov, and a son, Igor Ustinov. His third marriage was to Helene du Lau d'Allemans, which lasted from 1972 to his death in 2004.

Ustinov was educated at Westminster School and had a difficult childhood because of his parents' constant fighting. One of his schoolmates was Rudolf von Ribbentrop, the eldest son of the Nazi Foreign Minister Joachim von Ribbentrop. While at school, Ustinov considered anglicising his name to "Peter Austin", but was counselled against it by a fellow pupil who said that he should "Drop the ‘von’ but keep the ‘Ustinov’". After training as an actor in his late teens, along with early attempts at playwriting, he made his stage début in 1938 at the Players' Theatre, becoming quickly established. He later wrote, "I was not irresistibly drawn to the drama. It was an escape road from the dismal rat race of school."