Walter Russell Brain, 1st Baron Brain (23 October 1895 – 29 December 1966) was a British neurologist.
He was principal author of the standard work of neurology, Brain's Diseases of the Nervous System, and longtime editor of the homonymous neurological medical journal titled Brain.
He is also eponymised with "Brain's reflex", a reflex exhibited by humans when assuming the quadrupedian position.