Not just based off, but in some cases blatant ripoffs. Shakespeare was famous for swiping the plots of Italian plays. Ever notice how many of his plays are set in Italy? This was before "remix" was a word.

Shakespeare's specialty was writing clever dialog (and to give credit where it's due, he was very, very good at that), not coming up with totally original plays.

If copyright as we know it had existed in Shakespeare's time, he would have been sued into a smoking crater.