Complex sentence: Planck made many contributions to theoretical physics, but his fame as a physicist rests primarily on his role as an originator of the quantum theory, which revolutionized human understanding of atomic and subatomic processes.
Split into simpler sentences: Planck made many contributions to theoretical physics, but his fame as a physicist rests primarily on his role as an originator of the quantum theory. Max Planck's quantum theory revolutionized human understanding of atomic and subatomic processes.