What is the role of Demogorgon in Prometheus Unbound?

Shelley's Demogorgon in Prometheus Unbound is a prime example of a reversal of the roles of good and evil, light and dark. Demogorgon is the sole character capable of overthrowing the unjust tyrant Jove, despite his demonic origins. Shelley is making a profound statement here that authority is not necessarily a force for good and darkness not entirely evil. We should questions the long-standing reign of our gods and in a political sense, our dictators. In the natural state of society, the potential of divine love should win out over greed and evil. Demogorgon may be a dark character but he tells us that Jove reigns simply because love does not currently prevail in mankind.
Demogorgon is a character who represents the primordial and is therefore outside the fate and control of both Prometheus and Jove. Shelley places the mysterious Demogorgon on his invisible throne at the bottom of a cave, far from heaven. This cave is a metaphor for the underworld as well as the forgotten powers of the primordial earth. His role as a powerful truth-teller is essential in the glorification of the sublime in man and nature. Through Demogorgon, man achieves his highest potential through freedom and balance.

In Prometheus Unbound, Demogorgon is a spirit from the underworld who challenges and ultimately dethrones his father, Jupiter. In literature, Demogorgon is traditionally presented as a diabolical character. Yet Shelley, true to his radical political beliefs, makes Demogorgon a force for good, a force that brings love and harmony to the cosmos.
Demogorgon's usurpation of his father is an allegory of revolutionary political change, the kind which Shelley enthusiastically endorsed. Shelley portrays Jupiter as a vengeful, sadistic tyrant, and it's not hard to see in this portrayal a reflection of Europe's ruling classes. Jupiter wants to keep humankind in ignorance and fear, the better to overawe and control them. This is precisely what Shelley accused the ruling classes of doing to the common people.
Etymologically, Demogorgon derives part of its name from the Greek word demos, meaning "people." (This root is also where we get the word "democracy" from). In that sense, Demogorgon symbolizes the common folk, the poor, oppressed masses, rising up from the depths of darkness and ignorance to overthrow the tyrannical power that has kept them in subjection for so long.