Sir Aaron Klug, OM, PRS (born 11 August 1926) is a Lithuanian-born British chemist and biophysicist, and winner of the 1982 Nobel Prize in Chemistry for his development of crystallographic electron microscopy and his structural elucidation of biologically important nucleic acid-protein complexes.

He later graduated with a degree in science at the University of Witwatersrand and studied crystallography at the University of Cape Town before moving to England, completing his doctorate at Trinity College, Cambridge in 1953.
In late 1953, he started working with Rosalind Franklin in John Bernal's lab. This experience aroused a lifelong interest in the study of viruses, and during his time there he made discoveries in the structure of the tobacco mosaic virus. In 1962 he moved to the newly built MRC Laboratory of Molecular Biology in Cambridge. Over the following decade Klug used methods from X-ray diffraction, microscopy and structural modelling to develop crystallographic electron microscopy.
He was awarded the Louisa Gross Horwitz Prize from Columbia University in 1981. Between 1986 and 1996 he was director of the Laboratory of Molecular Biology in Cambridge, and was knighted by Queen Elizabeth II in 1988. He was elected President of the Royal Society, and served from 1995-2000. He was appointed OM in 1995 - as is customary for Presidents of the Royal Society.
In 2005 he was awarded South Africa's Order of Mapungubwe (gold) for exceptional achievements in medical science.