The famous physicist known for his theories on the photoelectric effect is Albert Einstein. In 1905, he proposed that light can behave as both a wave and a particle, leading to the concept of photons. His work on the photoelectric effect demonstrated that light can eject electrons from a material, a phenomenon crucial to the development of quantum theory. This groundbreaking discovery earned him the Nobel Prize in Physics in 1921. Einstein's theories not only advanced our understanding of light but also paved the way for future research in quantum mechanics and revolutionized theoretical physics.