In older literature, there seems to be a lot of characters that are somehow masters of disguise. In Jane Eyre, the tall, rich landowner character disguises himself as a small, raggedy witch prophet who actually predicts the future. He tricks an entire party of people, people that he has met before, and who recognize him when he removes his disguise. In King Lear, there are multiple instances of characters dressing up as different people, those instances being Kent and Edgar (and the Fool kind of), and not leaving anyone in the room unconvinced of their false identities.
Similarly to the characters in physical disguises, the evil characters are masters at hiding their motives. These characters are Regan, Goneril, Cornwall, Edmund, and even Oswald. This sets up the heroes and the villains: the heroes are in disguise and the villains are lying. Kent is wholly good, and Regan is wholly bad. This leaves another category of characters: the ones who don’t know what’s happening. Lear, Gloucester, and Albany all get screwed over in this play, and while Shakespeare uses themes and metaphor to portray these downfalls, the literal reason why is due to political incompetency.
Shakespeare uses the motif of disguises to create plenty of interesting conflict, as well as move the play along. The situations created by characters pretending advances Lear’s falling into madness, the war between Britain and France, and other key plot points. Also, it’s fun to see situations such as Edgar pretending not to be talking to his father. There’s no way Edgar could ever be as good of an impersonator as he is in this scene, even while speaking to a blind man, but it’s about the hypothetical and the ideas being presented. For example:
Edgar Ten masts at each make not the altitude Which thou has perpendicularly fell. Thy life's a miracle. Speak yet again. Gloucester But have I fall'n or no? Edgar From the dread summit of this chalky bourn. Look up a-height. The shrill-gorged lark so far Cannot be seen or heard. Do but look up. Gloucester Alack, I have no eyes. Act 4, Scene 6, Line 67
In this excerpt, Edgar pretends to be not Edgar, while also pretending to be at the bottom of a mountain rather than at the top of one. And he convinces Gloucester of this by, while staring into the bloody red abyss that was previously the home of Gloucester’s eyeballs, tells Gloucester to “Look up”. He awes at the sight of the tall mountains, describing a scene that Gloucester can’t see. This trick would never work in real life, but this isn’t real life, it’s a theatre. Shakespeare uses disguises to explore interesting scenarios while developing characters: from this scene, we have learned that Edgar is cunning in his goodness (as opposed to Edmund) and that Gloucester’s safety is and will always be reliant on the actions of others.