Albert Einstein was a German-born theoretical physicist who is widely regarded as one of the most influential scientists of the 20th century. He is best known for developing the theory of relativity, which revolutionized our understanding of space, time, and gravity. Einstein also made significant contributions to the development of quantum mechanics and statistical mechanics, and he was awarded the Nobel Prize in Physics in 1921 for his work on theoretical physics. Later in life, he became an outspoken pacifist and civil rights activist. Einstein died in 1955 at the age of 76.