Napoleon Hill was an American author who was one of the earliest producers of the modern genre of personal-success literature. His most famous work, Think and Grow Rich, is one of the best-selling books of all time. In America, Hill stated in his writings, people are free to believe what they want to believe, and this is what sets the United States apart from all other countries in the world. Hill's works examined the power of personal beliefs, and the role they play in personal success. "What the mind of man can conceive and believe, it can achieve" is one of Hill's hallmark expressions. How achievement actually occurs, and a formula for it that puts success in reach for the average person, were the promise of Hill's books.