The influential physicist known for developing quantum theory is Max Planck. His groundbreaking work in 1900 introduced the concept of quanta, suggesting that energy is not continuous but rather emitted in discrete packets, later termed photons. This revolutionary idea fundamentally altered the understanding of physics and paved the way for the development of modern quantum mechanics. Planck's contributions earned him the Nobel Prize in Physics in 1918, establishing a foundation for theories that elucidate behaviors at the atomic and subatomic levels. His work remains essential in fields ranging from particle physics to quantum computing.