The "Plunge Protection Team" was the nickname given, by The Washington Post in 1997, to Executive Order 12631, signed by Ronald Reagan. It is also known as The President's Working Group on Financial Markets. The The group was created in response to the 1987 market crash.
The group consists of the Secretary of the Treasury, the Chairman of the Board of Governors of the Federal Reserve, the Chairman of the SEC and the Chairman of the Commodity Futures Trading Commission.
Some observers believe the Working Group is in charge of secret manipulations of markets, such as the US stock markets and the gold market, especially during times of panic and high volatility.