The title of the number one diamond seller in the world is typically associated with De Beers Group. De Beers is one of the world’s largest and most influential diamond mining and trading companies. It has a long history in the diamond industry and has played a pivotal role in shaping the global diamond market.

De Beers is known for its extensive diamond mining operations, primarily in Botswana, Canada, Namibia, and South Africa. The company has a significant share of the rough diamond market and also operates in the retail sector through its subsidiary, De Beers Jewellers.

It’s important to note that the diamond industry is dynamic, and rankings and market share can change over time due to various factors, including shifts in diamond production, trading, and retailing. Different companies and groups may have the largest market share in specific segments of the diamond industry, such as rough diamond mining, diamond cutting and trading, or diamond jewelry retail.

For the most up-to-date information on the leading diamond sellers in the world, it’s advisable to consult industry reports and research from reputable sources, as market dynamics can change over time.