Final answer:
Niels Bohr significantly contributed to the quantum-mechanical model of the atom by introducing quantized energy levels, earning him a Nobel Prize in Physics.
Step-by-step explanation:
The scientist who played a major role in the development of the quantum-mechanical model of the atom is Niels Bohr. His work built upon that of Ernest Rutherford's planetary model. Bohr's novel introduction of quantized energy levels for the electron in an atom revolutionized atomic theory and laid the groundwork for modern quantum mechanics. He received the Nobel Prize in Physics for his pioneering contributions to our understanding of atomic structure and line spectra emissions.