The story of Gloucester and his two sons runs in parallel to the main story of Lear and his three daughters: essentially, the Gloucester story is a B-plot which helps to further illuminate the A-plot. This is a structure currently found today in everything from movies to episodic television, and it works for Shakespeare, too. Because the stories are analogous, the similarities and differences between them make us think more closely about what has gone wrong.

Lear is a very elderly man, and he is convinced that it is his "pelican daughters" who are entirely at fault for their betrayal of him. However, he is also beginning to suffer from senility, which develops throughout the play, and he is very susceptible to flattery. Because he does not know his children well, he expects that his favorite daughter, Cordelia, will tell him what he wants to hear. But he does not realize how strong her moral backbone is, much as he does not realize that if he gives power willingly to his other daughters, Regan and Goneril, they will not, in fact, look after him, but will oust him into the rain and cold without a care.

Gloucester, too, struggles to recognize the true moral characters of his sons. He does not realize that the way he has treated Edmund, his illegitimate son, has caused Edmund to become manipulative and resentful. He also has such little understanding of his first born, Edgar, that he is taken in by Edmund's machinations and willingly disinherits his own favored child.

At the end of the play, the "good" children, Edgar and Cordelia, both prove that they never did betray their fathers, but in each case it is too late. Their fathers' lack of knowledge or trust in their own children has caused their demise. Although in Lear's case, he willingly gives his power away, whereas in Gloucester's case, his son Edmund initiates the power grab, their stories are very alike.

To some extent, the stories of King Lear and Gloucester run parallel to each other. For one thing, neither man seems to understand his children. That explains why Gloucester openly makes fun of his son Edmund and why Lear foolishly divides his kingdom between his daughters. Such behavior will come back to haunt them in due course.

And therein lies another similarity between Lear and Gloucester: they are both betrayed by their children. Lear is betrayed by Regan and Goneril, and Gloucester by the child he calls a “whoreson,” Edmund. In the cut-and-thrust game of politics, the children prove themselves much more ruthless than their fathers.

As they don't really know their children, Lear and Gloucester are tragically unaware of which of their brood really loves them. Lear banishes Cordelia, the only one of his daughters who loves him, because she wouldn't make a public profession of love. Gloucester tries to execute Edgar, a decent, honest man, while trusting the inherently untrustworthy Edmund.

The main difference between the two men is that Lear willingly gives away his power, whereas Gloucester's is forcibly taken from him. If Lear hadn't divided up his land between his daughters, then they wouldn't have had the power to destroy him. Whereas Edmund deliberately sets out to destroy Gloucester, Regan and Goneril are opportunists who've been handed the opportunity to destroy their father by the man himself.

Lear and Gloucester are both very similar in that they are betrayed and stripped of power by their children. Both wander as outcasts after having been powerful and high status people.

A chief difference is that Lear willingly gives away most of his power to his two eldest daughters based on their empty words. He has been in charge and deferred to for so long that it never occurs to him that this situation could end—it seems as natural as the sun rising in the dawn. As his Fool points out to Lear after he divides his kingdom, he is a bigger fool than the Fool himself. With his eyes open (if not seeing), Lear create the situation that puts him in his daughters' power.

Gloucester, in contrast, is manipulated by Edmund without any realization of what is going on until it is too late. He does not put willingly power into this illegitimate son's hands and hope for the best: he is deceived by his son in underhanded ways. He is trusting, but he trusts what appears to be the evidence of his senses: Edgar, to any rational person, might seem to be a traitor because of the way Edmund manipulates events. Here, Edmund creates the situation that strips Gloucester of power.

While both men are the victims of ungrateful and evil children, they react differently. Lear, who does not like to give up his illusions, retreats into madness to avoid fully dealing with his new reality. Gloucester, though blinded, gains insight. He faces reality, and therefore, wishes to commit suicide, though Edgar prevents it.

Here are some basic similarities and differences to jump start you into a more detailed character analysis of each.

Similarities:

• Both have children whose love and loyalty are in question.
• Both fail to see, at the play's outset, which child is true and loyal and which is disloyal and false.
• Both are old men who, rather than enjoy the status and ease of their age and rank, are turned out into the wild and harsh elements to make their way in the world.
• Both Lear and Gloucester are reduced to despair about life and their situations.

Differences:

• Though they both are reduced to despair, Lear's desire to escape from reality manifests as madness, Gloucester's as thoughts of suicide.
• Gloucester's true/loyal son, Edgar, is able to assist his father through much of the events of the play, Lear's true/loyal daughter, Cordelia, arrives at the end and is not able to save Lear.
• Gloucester is literally blinded in the play, while Lear's blindness is figurative.

I hope that these general comparisons help you hone in on the details that you need!