Kwouk made his film debut in the 1957 film Windom's Way. One of his earliest film roles was in The Inn of the Sixth Happiness (1958) where he played the leader of a prison revolt who later aids the main character in heroically leading orphans to safety. He subsequently appeared in numerous films and television programmes. He was best known for playing Cato (originally spelled "Kato") Fong, Inspector Clouseau's manservant, in the Pink Panther film series. The character was first introduced in A Shot in the Dark (1964), the second film in the series, and was a role that Kwouk would reprise on another six occasions until the 2006 series reboot. The running gag was that Cato was ordered to attack Clouseau when he least expected it to keep him alert, usually resulting in a ruined romantic encounter or Clouseau's flat being completely destroyed. Amid the chaos, the phone would ring and Cato would calmly answer it with "Inspector/Chief Inspector Clouseau's residence", before dutifully handing the phone to his employer and being thumped by Clouseau.