Riazuddin, also spelled as Riaz-Ud-Din, was a Pakistani theoretical physicist, specialising in high-energy physics and nuclear physics. Starting his scientific research in physics in 1958, Riazuddin was considered one of the early pioneers of Pakistan's nuclear weapons development and atomic deterrence development. He was the director of the Theoretical Physics Group of the Pakistan Atomic Energy Commission from 1974 until 1984. Riazuddin was a pupil of the winner of the 1979 Nobel Prize in Physics, Abdus Salam.
Riazuddin carried out his research at the International Centre for Theoretical Physics, PAEC, the European Organization for Nuclear Research and Daresbury Laboratory where he published papers in mathematics and physics. Riazuddin also played an important role in education in Pakistan, contributing to the rise of science in Pakistan. Riazuddin authored several scientific books on particle physics and quantum mechanics. Later in his life, he joined the National University of Sciences and Technology as a visiting professor of theoretical physics.