JPMorgan sues ex-boss of "London Whale" JPMorgan Chase, the bank that lost at least $5.8bn through a massive credit derivatives position created by a trader nicknamed the "London Whale," has filed a lawsuit against his boss. The bank issued a claim in the High Court in London last week against Javier Martin-Artajo, court records show. Mr Martin-Artajo supervised Bruno Iksil, the trader who led the team that was allegedly responsible for the losses, and who was known by the monikers "Voldemort" and the "whale" for his outsize position. While the bank has filed its claim in court, it has not yet served it upon Mr Martin-Artajo, who will not have an opportunity to file his response until after that stage. This also means no details of the bank's arguments are publicly available. The bank has up to four months to serve its claim. Mr Martin-Artajo is "deeply disappointed" by the bank's action, said his solicitor, Greg Campbell at Mishcon de Reya. "Mr Martin-Artajo is confident that when a complete and fair reconstruction of these complex events is completed, he will be cleared of any wrongdoing," he said. There was no direct or indirect attempt by him at any time to conceal losses. JPMorgan declined to comment. The bank's London lawsuit, which was first reported by Bloomberg News, follows a pledge in July that it would attempt to claw back bonuses from the traders involved. The trading fiasco marred the bank's reputation for risk management and led to the resignation of Ina Drew, who ran the chief investment office. It sparked an internal investigation, regulatory inquiries, and in September caught the attention of the powerful US Senate subcommittee on investigations. In its most recent trading update earlier this month, JPMorgan reported a net income of $5.7bn for the third quarter and said there were further "modest" losses from unwinding credit derivatives on the London office's trading book. Mr Iksil and Mr Martin-Artajo have left the bank. The New York Times reported earlier this month that Mr Iksil has returned to his native France. The bank may not sue all the traders it alleges are responsible and has been in talks to attempt a voluntary return of bonuses. US authorities, including the Federal Bureau of Investigation, are probing JPMorgan over the situation. The UK's Financial Services Authority is investigating. Regulators are scrutinising JPMorgan's disclosure on an April call to investors that initially dismissed concerns over the position, as well as how traders in a London arm of the chief investment office were able to amass huge lossmaking positions. With additional reporting by Tom Braithwaite in New York