This simple slogan was launched in 1947, and is still in use today. The De Beers Diamond Company has used this unforgettable slogan in what is definitely one of the longest running ad campaigns of all time. De Beers has relied on the simple black-and-white advertisements to convey a feeling of timelessness in selling their pricey diamonds.

Perhaps the 1971 James Bond movie "Diamonds Are Forever" also helped to secure this slogan ("A Diamond is Forever") as a mainstay in society.

The woman who actually coined this famous advertising line "A Diamond is Forever" was Frances Gerety (1916–1999). She worked as a young copywriter for N. W. Ayer & Son.

To its great credit in the year 2000, Advertising Age magazine named "A Diamond Is Forever" the best advertising slogan of the 20th century.

More Info: en.wikipedia.org