Explore the fundamental concepts of Quantum Chromodynamics (QCD) and the physics of the Electron-Ion Collider (EIC) in this comprehensive lecture. Delve into the structure of hadrons, the distribution of quarks and gluons within nucleons, and the role of gluons in generating mass in the visible universe. Examine how the EIC will investigate the spin composition of protons and the potential for gluon saturation in heavy ion collisions. Learn about the unprecedented level of detail the EIC will provide in probing nucleon structure, offering access to previously unseen information. Gain insights into the key questions driving EIC research and the potential for groundbreaking discoveries in particle physics, hadron physics, and heavy ion physics.