Often credited as the greatest comedian of all time, Peter Sellers was born Richard Henry Sellers to a well-off acting family in 1925 in Southsea, a suburb of Portsmouth. He was the son of Agnes Doreen "Peg" (Marks) and William "Bill" Sellers. His parents worked in an acting company run by his grandmother. His father was Protestant and his mother was Jewish (of both Ashkenazi and Sephardi background). His parents' first child had died at birth, so Sellers was spoiled during his early years. He enlisted in the Royal Air Force and served during World War II. After the war he met Spike Milligan, Harry Secombe and Michael Bentine, who would become his future workmates.

After the war, he set up a review in London, which was a combination of music (he played the drums) and impressions. Then, all of a sudden, he burst into prominence as the voices of numerous favorites on the BBC radio program "The Goon Show" (1951-1960), and then making his debut in films in Penny Points to Paradise (1951) and Down Among the Z Men (1952), before making it big as one of the criminals in The Ladykillers (1955). These small but showy roles continued throughout the 1950s, but he got his first big break playing the dogmatic union man, Fred Kite, in I'm All Right Jack (1959). The film's success led to starring vehicles into the 1960s that showed off his extreme comic ability to its fullest. In 1962, Sellers was cast in the role of Clare Quilty in the Stanley Kubrick version of the film Lolita (1962) in which his performance as a mentally unbalanced TV writer with multiple personalities landed him another part in Kubrick's Dr. Strangelove or: How I Learned to Stop Worrying and Love the Bomb (1964) in which he played three roles which showed off his comic talent in play-acting in three different accents; British, American, and German.

The year 1964 represented a peak in his career with four films in release, all of them well-received by critics and the public alike: Dr. Strangelove or: How I Learned to Stop Worrying and Love the Bomb (1964), for which he was Oscar nominated, The Pink Panther (1963), in which he played his signature role of the bumbling French Inspector Jacques Clouseau for the first time, its almost accidental sequel, A Shot in the Dark (1964), and The World of Henry Orient (1964). Sellers was on top of the world, but on the evening of April 5, 1964, he suffered a nearly fatal heart attack after inhaling several amyl nitrites (also called 'poppers'; an aphrodisiac-halogen combination) while engaged in a sexual act with his second wife Britt Ekland. He had been working on Billy Wilder's Kiss Me, Stupid (1964). In a move Wilder later regretted, he replaced Sellers with Ray Walston rather than hold up production. By October 1964, Sellers made a full recovery and was working again.

The mid-1960s were noted for the popularity of all things British, from the Beatles music (who were presented with their Grammy for Best New Artist by Sellers) to the James Bond films, and the world turned to Sellers for comedy. What's New Pussycat (1965) was another big hit, but a combination of his ego and insecurity was making Sellers difficult to work with. When the James Bond spoof Casino Royale (1967) ran over budget and was unable to recoup its costs despite an otherwise healthy box-office take, Sellers received some of the blame. He turned down an offer from United Artists for the title role in Inspector Clouseau (1968), but was angry when the production went ahead with Alan Arkin in his place. His difficult reputation and increasingly erratic behavior, combined with several less successful films, took a toll on his standing. By 1970, he had fallen out of favor. He spent the early years of the new decade appearing in such lackluster B films as Where Does It Hurt? (1972) and turning up more frequently on television as a guest on The Dean Martin Show (1965) and a Glen Campbell TV special.

In 1974, Inspector Clouseau came to Sellers rescue when Sir Lew Grade expressed an interest in a TV series based on the character. Clouseau's creator, writer-director Blake Edwards, whose career had also seen better days, convinced Grade to bankroll a feature film instead, and The Return of the Pink Panther (1975) was a major hit release during the summer of Jaws (1975) and restored both men to prominence. Sellers would play Clouseau in two more successful sequels, The Pink Panther Strikes Again (1976) and Revenge of the Pink Panther (1978), and Sellers would use his newly rediscovered clout to realize his dream of playing Chauncey Gardiner in a film adaptation of Jerzy Kosinski's novel "Being There". Sellers had read the novel in 1972, but it took seven years for the film to reach the screen. Being There (1979) earned Sellers his second Oscar nomination, but he lost to Dustin Hoffman for Kramer vs. Kramer (1979).

Sellers struggled with depression and mental insecurities throughout his life. An enigmatic figure, he often claimed to have no identity outside the roles that he played. His behavior on and off the set and stage became more erratic and compulsive, and he continued to frequently clash with his directors and co-stars, especially in the mid-1970s when his physical and mental health, together with his continuing alcohol and drug problems, were at their worst. He never fully recovered from his 1964 heart attack because he refused to take traditional heart medication and instead consulted with 'psychic healers'. As a result, his heart condition continued to slowly deteriorate over the next 16 years. On March 20, 1977, Sellers barely survived another major heart attack and had a pacemaker surgically implanted to regulate his heartbeat which caused him further mental and physical discomfort. However, he refused to slow down his work schedule or consider heart surgery which might have extended his life by several years.

On July 25, 1980, Sellers was scheduled to have a reunion dinner in London with his Goon Show partners, Spike Milligan and Harry Secombe. However, at around 12 noon on July 22, Sellers collapsed from a massive heart attack in his Dorchester Hotel room and fell into a coma. He died in a London hospital just after midnight on July 24, 1980 at age 54. He was survived by his fourth wife, Lynne Frederick, and three children: Michael, Sarah and Victoria. At the time of his death, he was scheduled to undergo an angiography in Los Angeles on July 30 to see if he was eligible for heart surgery.

His last movie, The Fiendish Plot of Dr. Fu Manchu (1980), completed just a few months before his death, proved to be another box office flop. Director Blake Edwards' attempt at reviving the Pink Panther series after Sellers' death resulted in two panned 1980s comedies, the first of which, Trail of the Pink Panther (1982), deals with Inspector Clouseau's disappearance and was made from material cut from previous Pink Panther films and includes interviews with the original casts playing their original characters.