American Government and Politics in the Information Age: "Chapter 13: The Presidency"
Read this chapter. The United States was the first nation to create the office of president as the head of state in a modern republic, and today the presidential system of government is used in several countries. As of 2015, there have been 44 presidents of the United States. From the early 20th century, the United States' superpower status has made the President one of the world's best-known public figures. During the Cold War, the President was called the "leader of the free world", and since the collapse of the Soviet Union the President is often described as "the most powerful person on Earth".