Sir Dennis Weatherstone KBE (29 November 1930 – 13 June 2008) was the former CEO and chairman of J. P. Morgan & Co. Born in London, he attended North Western Polytechnic.

In 1946, at age 16, he was hired as a bookkeeper and was quickly promoted to the foreign exchange trading desk at the Guaranty Trust Company, a predecessor firm in London.

In 1990, he was named chairman and chief executive officer and was knighted by Queen Elizabeth II—the first J.P. Morgan employee to receive the honour.

A decade later, the Glass–Steagall Act was repealed, allowing banking companies to provide any service, whether it be a loan, advice or a securities offering.

The tool emerged in the wake of the 1987 stock market crash when Sir Dennis asked his division chiefs to put together a briefing to answer the question: "How much can we lose on our trading portfolio by tomorrow's close?"