The UK's Financial Services Authority (FSA) has imposed its highest fine to date on an individual.
Rameshkumar Goenka, a Dubai-based private investor, must pay $9.6m (£6m) for manipulating the value of shares in Indian industrial group Reliance.
Of the fine, $3.1m will reimburse an unnamed bank for the loss it suffered at Mr Goenka's hands.
It had sold Mr Goenka a structured product, the value of which depended on Reliance's closing share price.
In order to avoid a loss on the product, the FSA said the investor had "arranged for a pre-planned series of substantial and carefully timed orders to be placed in the final seconds of the [London Stock Exchange]'s closing auction".
Mr Goenka's fine would have been more than $12m, but was reduced by 30% after the investor agreed to settle the claim at an early stage.
"[Mr] Goenka's structured product was an investment that would have made him a considerable profit had it been successful for him," said Tracey McDermott, the FSA's acting director of enforcement.
"When he saw that it was not going to produce the desired result, [Mr] Goenka manipulated the market to avoid a substantial loss."