The term 'Quantum Theory Pioneer' refers to two scientists, Niels BOHR and Max Planck. Niels BOHR was a Danish physicist who made foundational contributions to understanding atomic structure and quantum theory. He proposed the BOHR model of the atom, which described the atom as having a small, positively charged nucleus surrounded by electrons that travel in circular orbits around the nucleus. Max Planck was a German physicist who is considered to be the founder of quantum theory. He proposed the Planck's law of black body radiation, which states that the energy of a system is quantized, or divided into discrete units. Both BOHR and Planck's work laid the foundation for modern quantum mechanics.