Gregory Evgenievich (Ezekielevich) Pikus (May 7, 1923 – April 12, 1998) was a prominent Soviet theoretical physicist whose contributions strongly influenced developing physics of semiconductors. Among his most fundamental contributions are development of the method of invariants in band theory of solids, the Bir-Aronov-Pikus mechanism of spin relaxation of electrons, prediction of the circular photogalvanic effect, and theory of weak localization in noncentrosymmetric structures. His three monographs reflect the focus points of the theory of semiconductors during the second half of 20th century from transistors to band theory to properties to artificial nanostructures.