PJ2:
Earlier this year, Hamilton Sundstrand delivered the first production Ram Air Turbine (RAT) to Boeing for the 787. In the extremely rare case of a loss of engine-generated power, the RAT deploys from the underside of the fuselage to produce both electricity for the cockpit and hydraulic power for the flight controls, allowing the aircraft to land safely. Hamilton Sundstrand is the world's leading supplier of RATs. Since the technology's inception, Hamilton Sundstrand RATs have saved more than 1,400 lives.
The above quote from Hamilton Sundstrand's website suggests the RAT contains both a hydraulic pump and an electrical generator. This may be required because the 787 is a 'More Electric' aircraft than previous Boeing or Airbus aircraft.