Albert Einstein was awarded the Nobel Prize in Physics in 1921 for his explanation of the photoelectric effect, which was crucial in establishing quantum theory. His groundbreaking work demonstrated that light can behave both as a particle and a wave, leading to significant advancements in physics. Although Einstein is widely known for his theory of relativity, the Nobel Committee recognized the photoelectric effect for its profound implications in understanding electromagnetic radiation and its interaction with matter. The prize solidified Einstein's reputation as one of the most influential physicists of the 20th century and contributed to the foundation of modern physics.