* The story of King Leir: The main plot of King Lear is based on the legendary story of King Leir, a figure from British mythology who is said to have ruled during the 9th century BC. This story was familiar to Shakespeare through various sources, including the works of Geoffrey of Monmouth and Holinshed's Chronicles.
* The influence of classical drama: Shakespeare was a great admirer of classical Greek and Roman drama, and King Lear shows the influence of these works in its themes, structure, and language. For example, the play's emphasis on the destructive power of passion and ambition recalls the tragedies of Sophocles and Euripides, while its use of rhetoric and wordplay is reminiscent of the comedies of Aristophanes and Plautus.
* Shakespeare's personal experiences: Shakespeare may also have been inspired to write King Lear by his own personal experiences. The play deals with themes of aging, family conflict, and the loss of power, all of which were issues that Shakespeare was grappling with in his own life at the time he wrote the play.
Ultimately, the inspiration for Shakespeare to write King Lear is likely to have been a combination of these and other factors. The play is a complex and multifaceted work of art, and its enduring popularity is a testament to Shakespeare's skill as a playwright and his ability to tap into universal human themes.