Founded 400 years ago by samurai-cum-Buddhist priest Masamoto Sumitomo, it built its prosperity on copper, supplying the emperors from massive deposits on Shikoku, the smallest of Japan's four main islands.
After the Allies dismantled the zaibatsu after the Second World War, powerful traders like Yasuo Hamanaka helped Sumitomo retain its grip on the copper market, in which it is now the world's biggest player.
Mr Hamanaka, known as "Mr Five Per Cent" for the amount of the market he controlled, cut a figure far removed from the mythical samurai image. Aged 48, he was the archetypal "man in a grey flannel suit", outwardly another of Japan's corporate salarymen - a journeyman albeit an immensely powerful one.
The bespectacled executive joined Sumitomo in 1970, spending his entire career in copper trading. Apart from a brief spell as a clerk at the London Metals Exchange, he has not left Tokyo.
By the end of the 1980s, he was also known simply as "The Man" for his grip on the market.Reuse content