Colonel Reginald Edward Harry Dyer, CB (9 October 1864 – 23 July 1927) was an officer of the Bengal Army and later the newly constituted British Indian Army. His military career began serving briefly in the regular British Army before transferring to serve with the Presidency armies of India. As a temporary brigadier-general, he was responsible for the Jallianwala Bagh massacre that took place on 13 April 1919 in Amritsar (in the province of Punjab). He has been called "the Butcher of Amritsar", because of his order to fire on a peaceful crowd. The official report stated that this resulted in the killing of at least 379 people and the injuring of over a thousand more. Some submissions to the official inquiry suggested a higher number of deaths.

Subsequently, Dyer was removed from duty and widely condemned both in Britain and India, but he became a celebrated hero among some with connections to the British Raj. Some historians argue the episode was a decisive step towards the end of British rule in India.