Although hundreds of people work on films, ranging from editors to costume designers to makeup artists, no one has more influence on the ultimate quality of the film than does the director. They are involved at every level of the filmmaking process from the screenwriting to casting to shooting and editing, the director is there at the beginning and end. Attempting to define something as subjective as "greatness" is probably flawed at its roots, fortunately, there are also few topics that spark more debate and are more enjoyable to think about than trying to quantify the merits of something that is somewhat unscientific and arbitrary. The closest thing to a formula I can think of for measuring a director's relative "greatness" is a combination of how much the director's style and films have influenced succeeding filmmakers, how well regarded were they by the filmmakers and critics of their time as well as modern critical opinions on their work, how well have their films held up both to audiences and critics, and the overall aesthetic of their filmography. In the future, I hope to write articles on dealing with the most important directors from Europe and Asia but to start off the series, we will start in the country most synonymous with moviemaking. To qualify, a director had to have either been born in America or immigrate their at a young age. There are a few exceptions such as Billy Wilder and Elia Kazan who grew up in foreign countries but who worked entirely in Hollywood and whose films are so uniquely "American" that to not include them would be a crime. On the flip side, filmmakers who are associated with Hollywood filmmaking but whose films aren't innately American, such as Alfred Hitchcock, Christopher Nolan, Charlie Chaplin, and David Lean, are not considered but will appear in my list of European directors. Although there are a number of brilliant young American filmmakers today, in an attempt for the list to capture the "hall of fame" of American directors as it were, only one director on this list debuted after 1980. In order to make it as objective as possible, my personal feelings about each filmmaker were not taken into account and rather, the list is more of a reflection on the impact of each filmmaker, how influential they have been, and the importance of their films in the cinematic canon.