Often, after making a name for themselves appearing in wacky or silly movies, comics will purposefully take on a more serious role, often in an attempt to show off their range. Comics like Jim Carrey, Adam Sandler and Robin Williams are all noted for their tendency to alternate between funny and more serious roles.
Sometimes, the experiments blatantly don't work out, with viewers unable to see their favorite funny performers in a new light. But other times, the decision to switch gears in favor of working in a drama pays off for a comedian, sometimes even resulting in award nominations or greater appreciation from acting peers (as when Eddie Murphy was nominated for an Oscar for Dreamgirls).
In ascending order, these are the best serious movies starring comedians, as ranked by film fans.