Albert Einstein was a theoretical physicist who developed the theory of relativity, one of the two pillars of modern physics (alongside quantum mechanics). His work is also known for its influence on the philosophy of science. He is best known to the general public for his mass–energy equivalence formula E = mc2, which has been dubbed "the world's most famous equation". He received the 1921 Nobel Prize in Physics "for his services to theoretical physics, and especially for his discovery of the law of the photoelectric effect", a crucial step in the development of quantum theory.

Here's a breakdown of his major contributions:

* Theory of Relativity: This theory revolutionized our understanding of space, time, gravity, and the universe. It consists of two parts:

* Special Relativity: Deals with the relationship between space and time, and how they are relative to the observer's motion. It led to the famous equation E=mc², which shows the equivalence of mass and energy.

* General Relativity: Explains gravity as a curvature of spacetime caused by mass and energy. It has important implications for understanding the evolution of the universe, the behavior of light near massive objects, and the existence of black holes.

* Photoelectric Effect: Einstein explained the photoelectric effect, which describes how light can knock electrons loose from a metal surface. This work earned him the Nobel Prize in Physics and helped lay the foundation for quantum mechanics.

* Brownian Motion: Einstein provided a mathematical explanation for Brownian motion, the random movement of particles suspended in a fluid, which provided further evidence for the existence of atoms and molecules.

Einstein's work continues to have a profound impact on our understanding of the universe and is essential for many modern technologies, such as GPS systems, nuclear power, and medical imaging.