Sir Robert George Mappin Fenwick KNZM KStJ (5 May 1951 – 11 March 2020) was a New Zealand environmentalist, businessman and professional director. He was born in Auckland, New Zealand. Fenwick co-founded the organic composting service Living Earth Ltd, the NZ Natural bottled water brand and Te Matuku Oysters. He held a number of board and advisory panel positions.
Fenwick was appointed leader of the Progressive Green Party in 1996 and campaigned to create a Maritime Park in the Hauraki Gulf. In 1998, he was a founding member of the BlueGreens, an environmental policy group within the New Zealand National Party.
Fenwick was knighted in the 2016 Queen's Birthday Honours.
Fenwick died on 11 March 2020 of cancer in Waiheke Island, New Zealand at the age of 68.