GenOn Energy Holdings, formerly Mirant Corporation, was a subsidiary of GenOn Energy, and is now a part of NRG Energy.

GenOn Energy, Inc., based in Houston, Texas, United States, is energy company that provides electricity to wholesale customers in the United States. The company is one of the largest independent power producers in the nation with more than 7,000 megawatts of power generation capacity across the United States using natural gas, fuel oil and coal. GenOn Energy was headquartered in the Reliant Energy Plaza in Downtown Houston. The company, formerly known as RRI Energy, acquired Mirant on December 3, 2010. The corporate names and logos of both RRI Energy and Mirant were retired.