Peter Sellers modeled the character of Clouseau on the trademark of a box of matches which includes an image of Captain Matthew Webb, who in 1875 became the first person to swim the channel (his heroic mustache and proud stance are both mimicked). To lose weight, Sellers took dieting pills for a year.
In the bath scene with Capucine and Robert Wagner, an industrial-strength foaming agent is used, which burned both of the stars' skin. Wagner, who was completely immersed at one point, became blind for four weeks.
The film was intended to have David Niven's character Sir Charles Lytton as the main character. However, Peter Sellers' portrayal of Inspector Clouseau was so loved by the crew (and later by the audience) it became his character this film and the sequels focused on.
The Pink Panther diamond is named not only for its color, but also for a tiny pink flaw shaped like a panther. The overall pink however would make the Panther a very rare Type-IIa diamond, in which some colors are absorbed not by impurities as in most other colored stones but by a misalignment of crystal structure at the molecular level caused by tectonic pressure during formation ('plastic deformation'). Though there are about a dozen large pink diamonds of name in the world, there has never been an actual "Pink Panther".
An animated Pink Panther was created for the opening credits because writer and director Blake Edwards felt that the credits would benefit from some kind of cartoon character. David H. DePatie and Friz Freleng decided to personify the film's eponymous jewel, and the Pink Panther character was chosen by Edwards from over a hundred alternative panther sketches. The Pink Panther introduced in the opening credits became a popular film and television character in his own right, beginning with the cartoon short The Pink Phink the following year.
The role of Simone Clouseau was offered to Ava Gardner and Janet Leigh before Capucine got the part. In her autobiography, Leigh states she turned it down because she had recently gotten married to her fourth husband Robert Brandt and didn't want to go off on location and away from her new husband for the duration of filming. Ava Gardner accepted the role but both her salary and personal demands were deemed unacceptable to the producers.
Wael Zuaiter, a PLO representative and translator assassinated in Rome by Israeli agents in retaliation for the 1972 Munich Massacre, played the waiter at the cocktail party as an extra. He is seen crossing the room after fadeout from the news headline "Rebels Demand Princess Return Fabulous Gem". Wael was the first target in Israel's Operation Wrath of God, and was portrayed by Makram Khoury in Steven Spielberg's Munich.
Peter Ustinov was originally selected for the role of Inspector Clouseau. However, in January 1963, Ustinov was fired because the Mirsch Company sued him for damages after being pulled out of production. During production in Rome, Peter Sellers replaced him and ended up playing Inspector Clouseau in all of the Pink Panther movies.
David Niven was hoping the Pink Panther would help launch a series of films for him akin to the Thin Man Series. Due to the focus of future films being placed on Peter Sellers' Inspector Clouseau, this never came to fruition. Niven would go onto play a parody of Thin Man Nick Charles, named Dick Charleston, in Neil Simon's Murder by Death.