Consider this from Michael Masnick at TechDirt:
If the current US Copyright Law had been in effect over Shakespeare, I think he could have been sued by many authors for copyright infringement for writing that masterpiece.
Count how many lawsuits there could have been just for King Lear alone:
Shakespeare’s play is based on various accounts of the semi-legendary Celtic mythological figure Lear/Lir. Shakespeare’s most important source is thought to be the second edition of The Chronicles of England, Scotlande, and Irelande by Raphael Holinshed, published in 1587. Holinshed himself found the story in the earlier Historia Regum Britanniae by Geoffrey of Monmouth, which was written in the 12th century. Edmund Spenser’s The Faerie Queene, published 1590, also contains a character named Cordelia, who also dies from hanging, as in King Lear.
Other possible sources are A Mirror for Magistrates (1574), by John Higgins; The Malcontent (1604), by John Marston; The London Prodigal (1605); Arcadia (1580-1590), by Sir Philip Sidney, from which Shakespeare took the main outline of the Gloucester subplot; Montaigne’s Essays, which were translated into English by John Florio in 1603; An Historical Description of Iland of Britaine, by William Harrison; Remaines Concerning Britaine, by William Camden (1606); Albion’s England, by William Warner, (1589); and A Declaration of egregious Popish Impostures, by Samuel Harsnett (1603), which provided some of the language used by Edgar while he feigns madness. King Lear is also a literary variant of a common fairy tale, in which a father rejects his youngest daughter for a statement of her love that does not please him.
The source of the subplot involving Gloucester, Edgar, and Edmund is a tale in Philip Sidney’s Countess of Pembroke’s Arcadia, with a blind Paphlagonian king and his two sons, Leonatus and Plexitrus.