Raj Kumar Pathria (born March 30, 1933) is a theoretical physicist, a Distinguished Professor Emeritus at University of Waterloo, and an Urdu poet. Pathria is known for his work on superfluidity in liquid helium, Lorentz transformation of thermodynamic quantities, an exact evaluation of lattice sums and finite-size effects in phase transitions. Pathria is also the author of a graduate textbook on statistical mechanics, whose fourth edition appeared in the year 2021. He also wrote a book on relativity that was published as a Dover edition in the year 2003. Early life Pathria was born in a middle-class Punjabi family to parents Ramji Das Pathria and Mela Devi Pathria in a small town named Ramdas, 28 miles to the north of Amritsar. He received his early education in a local high school and then joined the Hindu College, Amritsar for his FSc studies. He was placed on the 'Role of Honour' of that college in the year 1950. Career Pathria obtained his BSc Honours and MSc Honours degrees from Panjab University, Hoshiarpur in July 1953 and July 1954, respectively, and soon thereafter, at the invitation of Professor F.C. Auluck, joined the graduate school of Physics at the University of Delhi for his doctoral studies – which he completed in March 1957. In February 1958, he joined the University of Delhi as a lecturer in physics and in April 1961 got promoted to readership. In August 1964, he left Delhi to take up a visiting professorship at McMaster University in Canada. Even though his field of research at the University of Delhi was primarily statistical mechanics, Pathria, during that time, got fascinated with the subject of relativity and in 1963, with the friendly cooperation of the Hindustan Publishing Corporation (India), produced a book entitled The Theory of Relativity. This maiden attempt at book-writing resulted in fabulous reviews from far and wide, especially from Professor William McCrea – who himself was a celebrated author on this subject. In 1974, the Pergamon Press, Oxford produced a second edition of that book and in 2003 Dover Publications of New York took that book under their wings. In Canada, Pathria continued his research in the diverse field of statistical mechanics; at the same time, he gave graduate courses on that subject at McMaster University, Hamilton and the University of Alberta, Edmonton. In 1967, he returned to India to take up professorship of theoretical physics at the