Percy Bysshe Shelley is a rebellious English Romantic poet born into a wealthy landowning family. He actively rejects the secure life his parents envision, choosing instead to champion societal revolution and atheism. His personal life reflects his belief in constant change, marked by shifting romantic attachments and a profound fascination with the volatile nature of water and sailing.

The unidentified, genderless narrator of the poem "Mutability" serves as a confident but melancholy voice. This persona assumes the authority to speak on behalf of all people, observing how quickly human emotions and thoughts vanish. The speaker views human existence as entirely subject to the unpredictable forces of nature and time.

Mary Goodwin is the daughter of radical thinkers and becomes a central figure in Shelley's unconventional social circle. She goes on to write the classic horror novel Frankenstein, a text that incorporates lines from Shelley's poetry and reflects similar ideas about unpredictable forces. She raises children with Shelley while maintaining a somewhat scandalous household.

Harriet Westbrook is the daughter of a coffee house owner who marries Shelley when she is just sixteen years old. She shares two children with the poet before he leaves her for another woman. Her relationship with Shelley demonstrates the harsh, real-world consequences of his belief in constant change.

Humanity serves as the collective subject of the poem. The text portrays people as unstable creatures who are entirely at the mercy of their environment, unable to hold onto a consistent thought or feeling for very long.

Timothy Shelley is a member of Parliament and a wealthy English landowner. He represents the established, stable upper-class society that his son actively rejects and campaigns against.

William is a relatively radical thinker who maintains an ongoing relationship with Shelley. He provides an intellectual background that shapes his daughter's unconventional life choices.

Claire Clairmont is Mary Goodwin's stepsister. She lives within the poet's eccentric social circle, participating in a lifestyle that openly defies 19th-century English social expectations.

Lord Byron is a prominent English poet who writes the rambunctious epic Don Juan. He spends time socializing with the Shelley household, sharing their belief in the supremacy of change and their rejection of standard social rules.

Victor Frankenstein is a fictional chemist who builds a living creature out of dead body parts. His experimental narrative serves as a warning about what happens when individuals try to usurp natural order and control life.