E. C. G. Sudarshan is widely regarded as the most gifted theoreticalphysicist of Indian origin in the latter half of the 20thcentury. This article describes his early student years in India,and at the Tata Institute of Fundamental Research inBombay, before he left for USA in 1955 to work with R. E.Marshak at the University of Rochester. It then recounts hiscareer as it evolved thereafter, and his decision to settle there.His contributions in many areas of physics, in each of whichhe made a distinct mark, are recalled. In particular, his workon the V – A theory of the weak interactions, and on the DiagonalRepresentation in quantum optics, are described insome depth and detail. Sudarshan maintained strong linkswith the Indian physics and scientific communities all his life.Fromthe 1970s onwards, he was at the Indian Institute of Sciencein Bangalore, and then at the Institute of MathematicalSciences in Madras, till 1990. The events of this period arerecounted. Some remarks on his personality, and his viewson life and philosophy, conclude the article.

The creation of quantum mechanics is one of the most dramatic developments in thephysics of the 20th century. After the period 1900–1924, during which the Law of BlackBody Radiation, wave particle duality for light and formatter, the general quantisation ofenergy and stability of matter and the laws of spectroscopy had begun to be understood,the mathematical structure of quantum mechanics was discovered amazingly rapidly injust under two years, 1925–1927. On the other hand, the physical interpretation andmeaning of this structure required an enormous effort, in which the uncertainty and complementarityprinciples, the Born probability interpretation and rule and the wave functioncollapse idea, all played important roles. While quantum mechanics has all alongbeen amazingly successful in numerous applications, many puzzling questions about interpretationremain and continue to be pursued till today, though the focus has shiftedfrom wave particle duality to entanglement and its signatures and consequences. This article gives an impressionistic account of these developments, accompanied by comments on the origins of human intuition and the meaning of human understanding of nature

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