Every generation has its share of actors who stand above the rest. The silent era had Chaplin and Keaton, who led to James Cagney and Humphrey Bogart, who led to Jimmy Stewart and John Wayne, and so on and so on. It might not seem like it, but there are many young actors working right now who possess the potential to one day be mentioned in the same breath as those film legends. To qualify for the list, the actors had to be under 40, ruling out modern legends like Daniel Day-Lewis and Robert De Niro, and they must possess the right mix of critical acclaim and box office success. The box office matters in this case because this isn't a list of the "ten best actors under 40", rather this is a list of the actors under 40 who have the best chance of being fondly remembered 50 or 60 years from now. They were ranked according to their acting ability including their versatility, believability, intensity, and charisma, as well as whether or not they have been in movies that will stand the test of time and whether or not they seem likely to continue being prominent actors for some time.