Professor Raj Kumar Pathria (born March 30, 1933) is a theoretical physicist and an Urdu poet.Pathria is known for his work on Superfluidity in liquid helium, Lorentz transformation of thermodynamic quantities, a rigorous evaluation of lattice sums and finite-size effects in phase transitions.Pathria is also the author of a graduate text book on Statistical Mechanics, which has recently appeared in its third edition. He also wrote a book on Relativity that has been published in a Dover edition.