King Lear is a play that explores the relationship between appearance and reality, and the tragic consequences of trusting in appearance more than reality.
Lear divides his kingdom between his two eldest daughters, because they express their undying love and devotion to him in exaggerated language. Cordelia, who is disgusted by her sisters' phoniness, refuses to flatter her father, so in a rage, he disinherits her and banishes her. She marries the King of France, who will later lead an army against her sisters.
Lear very soon learns that his older two daughters' words were empty promises made simply so they could seize power. Once they have his land and goods, he becomes a nuisance. They humiliate him and cast him aside.
In a parallel plot, the Earl of Gloucester is manipulated by his illegitimate son, Edmund, into thinking that his real son, Edgar is plotting against him. Both powerful men are humbled by their realization that they were deceived.
By the end of the play, both Lear and the Earl of Gloucester have learned the hard way who is faithful to them. In acts of poetic justice, Goneril and Regan are deceived by Edmund, Goneril kills Regan then commits suicide, and Edgar kills Edmund. Cordelia is hanged by Edgar's decree, and Lear dies of sorrow. Nevertheless, order is restored in the kingdom.