An overview of the history of projective representations (spin representations) of groups

Abstract: An overview of the history of projective representations (= spin representations) of groups, preceded by the prehistory of studies on the theory of quaternion due to Rodrigues and Hamilton. Beginning with Schur, we cover many mathematicians until today, and also physicists Pauli and Dirac. This is a self translation of Appendix A of my book "Introduction to the theory of projective representations of groups" in Japanese, 2018, Sugakushobo, and may serve as an introduction to our paper arXiv: 1804.06063 [math.RT] which will appear in Kyoto J. Math.