Charmonium, exotic hadrons and hadron structure

To celebrate the 50th anniversary of the discovery of the J/ψ, the first charmonium state observed, I start with a brief review of major progresses on the QCD inspired quark potential model originated from charmonium spectrum.Then I show the importance of unquenching dynamics, multiquark components and exotic multiquark states for understanding hadron structure and hadron spectrscopy. The J/ψ and charmonium-like states have played an important role in this aspect.