The term “Byronic hero” is derived from George Gordon, Lord Byron, an English writer and politician who lived from 1788 to 1824. The term is applied to heroes of Byron's works, such as Childe Harold’s Pilgrimage, and to other literary figures (generally men) who resembled Byron or characters in his works. The Byronic hero is a hallmark of Romanticism in its English variant, especially its earlier years.

The Byronic hero is a noble but flawed, and often doomed, figure. The Romantic ideal of acting out of romantic love or out of pure motives to support a cause frequently cannot be achieved in real life. But the Byronic hero suffers and sacrifices for that love or those causes. Taking an individual stand against oppressive society places him outside the bounds of conventional life. The fact that Byron himself died young, fighting for Greek patriotic causes, is one reason his name is attached to such heroes.

In Prometheus Unbound, Shelley expands on the myth of Prometheus and draws on the classic Greek play by Aeschylus. Prometheus is a hero to humankind because he gave them fire. But this act is not seen as heroism by the gods. Fire was not really his to give; he stole it from the most powerful god, Jupiter. In this respect, as a flawed hero acting for the greater good of humankind, Prometheus is Byronic. This hero was intended

To suffer woes which Hope thinks infinite;
To forgive wrongs darker than death or night;
To defy power which seems omnipotent . . .

In Shelley’s tale, unlike in its classical versions, Jupiter is not justified in punishing Prometheus. For the ancient Greeks, Zeus (whom the Romans called Jupiter) was omnipotent, and to challenge him was guaranteed to end badly. For Shelley, writing post-Enlightenment, individual freedom and challenges to authority were deeply held values. Shelley’s Prometheus, the Byronic rebel figure, ultimately suffers torment on Jupiter’s orders. This support of revolutionary causes over old established ways can be seen in Demogorgon’s defeat over Jupiter and in this defeat's liberation of Prometheus.

Prometheus is a Byronic hero to the extent that he chooses to defy prevailing conventions and assert his own personality irrespective of the consequences. Prometheus has made the conscious choice to challenge the authority of mighty Zeus by stealing fire from the gods and giving it to man. Prometheus is completely alone in his rebellious endeavor, and his isolation is another characteristic one associates with the Byronic hero.

One additional feature of the Byronic hero is his immense suffering. Byronic heroes like Manfred, and Prometheus as envisaged by Shelley, suffer greatly as a result of their defiance. More than anything else, this is what makes them truly heroic. Prometheus knew full well what was in store for him when he stole fire from the gods, but he went ahead and did it anyway. He knew that the angry Zeus would make him suffer for his gross impertinence. But Shelley's Prometheus is presented almost as a Christlike figure who is willing to sacrifice himself for the good of mankind. In this sense, he is not quite as dark, brooding, or as individualistic as the traditional Byronic hero—again, the example of Manfred springs to mind—but the end result of his sacrifice is the same: immense suffering on an unimaginable scale.

When we consider the traits of the Byronic Hero, we gain a composite sketch of the figure who believes in self sacrifice. We can see this in the mere selection of Prometheus as a subject.  The God who was punished for giving fire to man and teaching individuals how to trick the gods received punishment for a crime that did not benefit him, but rather gave profound benefit to others.  When the reader is introduced to Prometheus, his crime is unnamed, remaining consistent with another Byronic Heroic trait.  The treatment of Prometheus is consistent with that of an outsider, or someone who experiencing the wrath of the social order.  This is yet another trait of the Byronic vision of the protagonist.  One significant difference is that the Byronic Hero is one who is condemned to suffer and almost wallows in it.  The grace shown to Prometheus with the overthrow of Zeus and gaining his freedom in Shelley's poem is an aspect that is not entirely consistent with the Byronic Hero.