The primary speaker of the poem acts as an inquisitive and distressed observer of the Lisbon earthquake. He aggressively challenges the prevailing philosophical theory of optimism. He uses graphic descriptions of death to dismantle the idea that humans live in the best of all possible worlds. As the argument progresses, his tone shifts from angry to emotionally exhausted. He relies on sensory evidence and human empathy to argue his points.

The interlocutor in the dialogue gives voice to the philosophical theory of optimism. He attempts to justify the disaster as an essential part of a larger divine plan. He operates under the assumption that a benevolent deity cannot create pure evil. He maintains that partial human suffering ultimately leads to a general universal good.

The supreme being and creator of the universe sits at the center of the theological debate. His nature is constantly questioned in light of the horrific destruction of the earthquake. He holds the eternal chain of fate and possesses the power to direct nature's course.

The spectator represents the audience or the unaffected observers of the Lisbon disaster. The poem directly addresses this group by noting their calm tranquility as they watch the suffering of others. The speaker challenges them to abandon their intellectual detachment and embrace their shared human vulnerability.

An Islamic spiritual leader who appears in a brief story at the very end of the poem. Facing his own death, he offers a humble prayer to the supreme being. He acknowledges human defects and ignorance, bringing to his creator everything that the divine lacks except for hope.

A real-world philosopher whose ideas are directly attacked within the text. He represents the theory of optimism, arguing that an omnipotent deity would not allow evil to exist without a greater purpose. The speaker targets his philosophical system as flawed in the face of physical devastation.