Reginald Edward Harry Dyer (October 9, 1864 - July 23, 1927) was a British colonial officer in India.

Under his command, 150 British troops killed 379 unarmed Indians and injured 1200 (though many Indians claim a death toll in the thousands) in the Amritsar Massacre of April 13, 1919. The pretext was the killing of four Europeans, and the beating of a woman missionary. The crowd was also illegally assembled in a park, participating in a political rally protesting the Rowlatt Acts. The meeting was on a religious holiday, Baisakhi. The park was walled, and had only one entrance, which the troops blocked. Naturally, the crowd was unable to comply with commands to disperse.

He commanded the brigade at Jullundur during the massacre. Although London society praised his ruthlessness, he was widely condemned internationally, and the Army forced him into retirement.

He was born in Murree, which was in India at the time, and is now in Pakistan. In 1885 he obtained a commission to the West Surrey Regiment. He then transferred to the Indian Army. He participated in a campaign in Burma, from 1886 to 1887. He assisted a blockade at Waziristan from 1901 to 1902. From 1914 to 1918 he commanded the Eastern Persian Cordon. His mission there was to prevent German troops and materiel from crossing into Afghanistan. Jullundur was his last command posting. He died in the United Kingdom at Long Ashton, near Bristol.