E.ON UK is a British energy company and the largest supplier of energy and renewable electricity in the UK, following its acquisition of Npower. It is a subsidiary of E.ON of Germany and one of the Big Six energy suppliers. It was founded in 1989 as Powergen, and was listed on the London Stock Exchange and was once a constituent of the FTSE 100 Index. It has been a subsidiary of E.ON since 1 July 2002.