theoldlibrarian said:
Of course none of his plots were in entirely original but that is an invalid argument seen as no plot is entirely original.
Back then, just about every play was based on an earlier source of some kind, whether historical, biblical or based a previous play. Audiences came to see works based on historical figures or stories they were familiar with, so a completely "original" story wouldn't have worked, commercially.
Aristophenes may have been the first playright to actually create plays with "original" stories (even though he used mythical and historical events as backdrops), but the comedians had a lot more latitude in this area.
J-I-B