Though this knave came something saucily into the world before he was sent for, yet was his mother fair, there was good sport at his making, and the whoreson must be acknowledged. (I.i.)

Gloucester is introduced as a jolly character, making jokes about his bastard son, Edmund. However, Edmund is standing right beside him, so the audience can see that these jokes are cruel. Gloucester’s blindness to the real feelings of his son Edmund brings about his downfall, just as Lear’s blindness to his daughters’ motivations causes his downfall.

I would not see thy cruel nails
Pluck out his poor old eyes. (III.vii.)

Gloucester says this to Regan moments before he is blinded. These lines help to underline the violence and cruelty of Gloucester’s blinding, and also to draw a connection between Gloucester’s literal blinding and Lear’s metaphorical blindness.

As flies to wanton boys are we to th’ gods
They kill us for their sport. (IV.i.)

Gloucester begins the play making cruel jokes about his son. As a result, he is blinded in the play’s greatest act of cruelty. In these lines, Gloucester declares that the world is simply a cruel place. The gods themselves are cruel. King Lear is Shakespeare’s bleakest play, suggesting that cruelty is a fact of nature.