Definition of 'Rogue Trader'
A trader who acts independently of others - and, typically, recklessly - usually to the detriment of both the clients and the institution that employs him or her. Rogue traders typically trade in high risk investments which can create huge losses but also large gains.
Investopedia explains 'Rogue Trader'
One of the most famous rogue traders is Nick Leeson, who was a derivatives trader at the Singapore office of Britain's Barings Bank. Leeson incurred heavy losses through the unauthorized trading of large amounts of Nikkei futures and options. Leeson took large derivative positions on the Nikkei which leveraged the amount of money at stake in the trades.
At one point Leeson had 20,000 futures contracts worth over $3 billion on the Nikkei. A large chunk of the losses came from the downturn in the Nikkei after a major earthquake in Japan caused a broad-based sell-off in the Nikkei within a week. Total loss to the 233-year-old Barings Bank was well over $1 billion and led to its eventual bankruptcy. Leeson was charged with fraud and served several years in a Singapore prison.