Stephen Sondheim was clean shaven for most of his early career, and though he produced good music and lyrics, his signature style didn't appear until the mid 1970s, with "Company" when he literally grew a beard, which he has kept ever since.
Believe it or not, even Shakespeare had to grow the beard to become the master we know him as today. With the possible exception of Richard III, most of his earliest efforts are considerably less polished (and as a result, less popular) than the more mature works that would come to establish his reputation as the best of all time. Most scholars would agree that he didn't really hit his stride till Romeo and Juliet, which was something like his eleventh play! ("Something like," because, given the spottiness of early modern publication records, it's impossible to say with absolute certainty when the Bard wrote anything.)