Diana Decker (born 1 September 1924), born Isabella C. D. Decker, is an American-born British former actress, singer, and television personality, who was popular from the 1940s to the early 1960s.
She was born to an American father and British mother in the United States, either in Hollywood, California, or in Queens, New York City. At the age of four, she moved to Britain with her mother.
Her first film appearance was in 1943, an uncredited role in San Demetrio London, and the following year she appeared in the musical comedy Fiddlers Three. Further film roles followed, including parts in The Root of All Evil (1947), When You Come Home (1948), Murder at the Windmill (1949), Saturday Island (1952), Will Any Gentleman...? (1953), and Is Your Honeymoon Really Necessary? (1953). She specialised in "dizzy blonde" roles in light comedy films and also played this stereotype in a small part in her most significant film appearance in The Barefoot Contessa (1954). In 1947 Decker was also one of the first performers to gain fame from a TV ad campaign, playing "Miriam" in a Pepsodent commercial, with the catch phrase "Irium, Miriam?"
In 1953 Decker appeared in the British television comedy series Before Your Very Eyes!, starring Arthur Askey, and also chaired some editions of the television quiz Film Fanfare during the 1950s. She continued to act in films including, A Yank in Ermine (1955), and The Betrayal (1957), and featured in several episodes of the television drama series The Vise.