In 1964 I showed that the exclusion principle, which Wolfgang Pauli introduced for electrons in atomic physics, plays an important role in the quark physics of hadrons. Gursey and Radicati placed the ground-state baryons in 56 of SU(6). In the naive quark model this is 3 quarks, each in a 6 of SU(6), in a symmetric state. Since quarks are spin-1/2 particles the quarks should be in an antisymmetric state. To remedy that mismatch I suggested that the fermion quarks carry a new three-valued charge, later called ``color,'' and that the 56 of SU(6) should also be a singlet of the new SU(3)color . My insistence that the exclusion principle should be obeyed, together with the work of Nambu and Han who gauged SU(3)color in 1965, led to quantum chromodynamics, which is now a central part of the standard model of particle physics.