Final answer:
Max Planck, a German physicist, developed the Quantum Theory in 1900, introducing the concept of energy quantization and has the Planck's constant named after him, which was fundamental to the development of quantum mechanics.
Step-by-step explanation:
The Quantum Theory was developed by the German physicist Max Planck in 1900, and he is renowned for his introduction of the revolutionary concept of energy quantization.
His work laid the foundation for quantum mechanics, a significant branch of physics that describes the behavior of matter and energy on the atomic and subatomic scales.
Planck proposed that energy could only be emitted or absorbed in discrete units, which he called 'quanta', and he introduced the Planck's constant, represented by 'h', as a fundamental constant in his equation E = hu, where E is energy and u is frequency.
This idea was pivotal in explaining the blackbody radiation spectrum and this contribution, along with others to the fields of theoretical physics and relativity, led to Planck receiving the Nobel Prize in Physics in 1918.