Otherwise known as Yasuo Hamanaka, Mr. Copper was a trader in the copper market who lost over $2.5 Billion for his employer, Sumitomo Corp. (in Japan). The losses amassed from unauthorized trading in secret accounts between 1985 and 1996.

He was also referred to as "Mr. 5%" because at one point he controlled 5% of the world copper market. Hamanaka's scandalous activities represent the greatest unauthorized trading loss in history.