Walter Robert Hadwen MRCS MRCP (3 August 1854 – 27 December 1932) was an English general practitioner, pharmaceutical chemist and writer.

Hadwen was recruited as a member of the British Union for the Abolition of Vivisection by its founder and then president Frances Power Cobbe who hired a private investigator to assess his credentials (he was a vegetarian and total abstainer, had a reputation as a "firebrand" orator and was held in "high local esteem").

[5] Hadwen's pamphlets on anti-vivisection are archived at the Special Collections Research Center in NC State University Libraries.

His bet was successful and he stated that "For my part I am quite satisfied with my trial of vegetarianism, and it would take more than mortal power to persuade me once again to make my stomach a graveyard for the purpose of burying dead bodies in.

"[5] In 1924, having applied his rejection of the germ theory of disease, and his refusal to use diphtheria anti-serum produced by inoculation of animals to the treatment of Nellie Burnham, a young girl, she died and he was tried for manslaughter by criminal medical negligence.