Peter Clive Thonemann (3 June 1917 – 10 February 2018) was an Australian-born British physicist who was a pioneer in the field of fusion power while working in the United Kingdom. Thonemann was born in Melbourne and moved to Oxford University in 1944, becoming one of the earliest researchers on the topic of controlled fusion. He led the fusion research at Oxford in its early years, before moving to the Atomic Energy Research Establishment (Harwell) in 1950. He led the ZETA reactor development at Harwell and announced its apparent success in 1958.