The scientist recognized for his contributions to quantum mechanics is Albert Einstein. He developed the theory of relativity, significantly influencing our understanding of physics, but is also known for his work on the photoelectric effect, which provided crucial evidence for quantum theory. Einstein's work helped establish the relationship between energy and matter, encapsulated in his famous equation, E=mc². His theories challenged classical mechanics and laid the groundwork for modern physics, influencing numerous later developments in the fields of quantum mechanics and theoretical physics.