What is Rogue Trader?

Legal Definition
A rogue trader is an employee authorized to make trades on behalf of their employer (subject to certain conditions) who makes unauthorized trades. It is most often applied to financial trading, when rogue professional traders make unapproved financial transactions.

This activity is often in the grey area between civil and criminal transgression, because the perpetrator is a legitimate employee of a company or institution, yet enters into transactions on behalf of their employer without permission.

In several cases traders have initially made very large profits for their employers, and bonuses for themselves, from trades in breach of the rules, and it has widely been said that employers turned a blind eye to transgressions due to the profits involved.

One famous rogue trader is Nick Leeson, whose losses on unauthorized investments in index futures contracts were sufficient to bankrupt his employer Barings Bank in 1995. Through a combination of poor judgement on his part, increasingly large initial profits, lack of oversight by management, a naïve regulatory environment, and an unforeseen outside event, the Kobe earthquake, Leeson incurred a US$1.3 billion loss that bankrupted the centuries-old financial institution.

The key factor determining the use of the term is lack of authorisation. There have been colossal financial losses and bankruptcies from what are considered to be catastrophically bad decisions by senior decision-makers in financial institutions, such as the bankruptcy of Lehman Brothers which necessitated the 2008 United Kingdom bank rescue package, but this is not described as rogue trading and is not punishable.

In the UK the term is also used to describe dishonest tradesmen such as double-glazing salesmen, second-hand car dealers, gas fitters, mechanics, roofers, plumbers and domestic rubbish collectors. A BBC Television programme exposing such practices was called Watchdog, which was later followed by Rogue Traders.
-- Wikipedia