Allan Roy Mackintosh, FRS (22 January 1936 – 20 December 1995) was a prominent Danish physicist and a leading authority on magnetism and neutron scattering, especially in the rare-earth metals. Mackintosh was known for his key role in stimulating solid-state physics research in Denmark and for his advocacy of international collaboration. Many of his former students now occupy leading academic and industrial posts in a variety of countries. As director of the Danish Atomic Energy Research Establishment from 1971 to 1976 he was a major force in Danish science policy and a prolific contributor to the public debate about nuclear power.