Kurt Friedrich Godel (1906-1978) was an Austrian logician, mathematician and philosopher. Later in his life he emigrated to the United States to escape the effects of World War II. One of the most significant logicians of all time, Godel made an immense impact upon scientific and philosophical thinking in the 20th century. Godel is best known for his two incompleteness theorems, published in 1931 when he was 25 years old. To prove this theorem, Godel developed a technique now known as Godel numbering, which codes formal expressions as natural numbers. He also made important contributions to proof theory by clarifying the connections between classical logic, intuitionistic logic, and modal logic.