As noted before, the two major sources for King Lear are Holinshed’s Chronicles and an anonymous play, The True Chronicle History of King Leir and his three daughters Gonerill, Ragan and Cordella.
However, there are a couple of other non-literary influences that may have played a part in Shakespeare’s creation of the play…
First up is an anti-Catholic book by Samuel Harsnet, a religious writer who would later become the Archbishop of York (well after Shakespeare’s death). In 1603, he published his attack on the Catholic church–A Declaration of Egregious Popish Impostures, to with-draw the harts of her Majesties Subjects from their allegeance, and from the truth of the Christian Religion professed in England, under the pretence of casting out Devils–which includes a numbers of tales of demonic possession. These tales include a number of the demon names Edgar references in his assumed role of Poor Tom: Obidicut, Hobbididence, Mahu, Modo, and Flibbertigibbet. Since Harsnet’s book was supposedly non-fiction, are we to believe Edgar’s guise of madness is a realistic one, at least as far as his Elizabethan audience is concerned? And if that’s the case, should modern directors take a page from this playbook and attempt to play both his faux and Lear’s real madness as “scientifically real” as possible?
There was also a contemporary news story that had enough notoriety that if it didn’t influence some aspect of Shakespeare’s tweaking of the Leir story into Lear, then at least his audience could have brought their own knowledge of it to the play. Sir Brian Annesley had been a follower of Queen Elizabeth (in some reports, he is referred to as an ex-servant), who in his retirement owned an estate of some value in Kent. Annesley had three daughters–the eldest, Grace (who married into the wonderfully named Wildgoose (also spelled “Wildgose”) family; the second Christian; and the youngest, the appropriately named “Cordell.” In 1603, the eldest daughter petitioned to have her father certified as incompetent because of senility so that she could take control of his affairs and estate. The youngest daughter attempted to challenge this petition, and while Annesely died in 1604, Cordell was able to prevail, and her late father’s last will and testament was honored, leaving the majority of family property to her.
There was another, earlier, news story may have also influenced Shakespeare. Some thirty years before, a former Lord Mayor of London, Sir William Allen–fearing that he had grown too old to successfully manage his properties–made the Lear-like decision to split his estate amongst this three daughters. He had arranged to split his time between the three daughters, but without a real-life Cordelia (or Cordell, in Annesley’s case) to defend him, the three–citing misuse of their servants–mistreated him, and Allen died alone and in misery.
It’s unclear how conscious Shakespeare was of these pseudo-sources, but their notoriety does seem to have influenced at least some aspects of his creation of King Lear from the Leir sources.