Harry Oppenheimer, chairman of De Beers for 27 years and the man behind the concept of diamond advertising, died recently at the age of 91. The Oxford-educated son of cartel founder Ernest, Oppenheimer joined the De Beers board in 1934 and stayed on for 60 years. In 1957, he succeeded his father as chairman of De Beers and sister company Anglo-American. He stepped down as De Beers chairman in 1984 and retired from the board in 1994, but De Beers executives said he still made his opinions known about the business.

“He retained until the end his sense of curiosity and fun and great love for the diamond business,” said his son, current chairman Nicky, in a statement. “I and many others will very much miss his wise counsel and warm friendship.”

For American jewelers, Harry Oppenheimer is best known for his 1938 revelation that diamonds could be advertised just like any other product, over the objections of some on the De Beers board who thought advertising would “cheapen” the diamond’s image. De Beers’ partnership-initiated by Oppenheimer-with advertising agency N.W. Ayer lasted nearly 60 years and led to the famed slogan, “A Diamond is Forever,” which the company still uses.

Oppenheimer also is credited with forging the partnership between De Beers and the government of Botswana that is the cornerstone of De Beers’ domination of the market.

He was a frequent critic of South Africa’s apartheid system-both as a member of Parliament in his youth and as a major backer of the Progressive Party, for years the country’s sole white opposition voice. He gave up his Parliament seat when he ascended to the De Beers chairmanship but continued his criticism of his country’s government, once calling the country’s leaders “a tiresome, obstinate lot.”

According to press accounts, until his death Oppenheimer still regularly visited Anglo-American headquarters. Upon his 90th birthday, he told a reporter: “I feel very well, and I certainly feel happy and content. I’ve had, and have, a happy marriage. I have children who are nice to me, I’ve got lots of grandchildren, and I even have two great-grandchildren. What more can one want?”

“Harry Oppenheimer was legendary as South Africa’s greatest businessman for most of his lifetime,” said managing director Gary Ralfe. “He had an exceptional intellect and capacity for learning and at the same time had a self-effacing modesty and concern for others.”