Virgilio materializes as Dante's spirit guide through the underworld. He is the historical Roman poet Publius Vergilius Maro, deceased before Christ's birth, dwelling in the virtuous pagans' section of Limbo known as the Hall of Kings. Beatrice summons him to aid Dante after Dante's entry into Hell.

As guide, he commands deep knowledge of Hell's structure, punishments, and inhabitants. He elucidates the symbolic torments within each circle—like the unbaptized in Limbo or the gluttonous devoured by Cerberus—and advises Dante on navigating perils. His role involves interpreting the moral weight of witnessed suffering, repeatedly cautioning against pity for the damned while underscoring divine justice. He offers strategic aid, such as directing Dante to allow Cerberus to swallow him for deeper descent. He actively shields Dante from hostile entities, including demons and vengeful souls encountered during their journey. At their first encounter, he bestows a protective ability termed his "first spell."

His background as a poet surfaces, particularly his authorship of the Aeneid, which featured its own underworld depiction. He references his life under Augustus Caesar and death prior to Christ's birth, lamenting his exclusion from Heaven despite foreseeing the Messiah in his writings. Confinement to Limbo results from his unbaptized state, though his virtuous life spared him active torment.

His relationship with Dante blends mentorship with detachment. While providing unwavering support and intellectual clarity, he maintains a measured demeanor, occasionally showing impatience at Dante's hesitation or excessive sympathy for sinners. His guidance remains strictly bounded to Hell and Purgatory; as a pagan soul, he cannot enter Paradise. His arc concludes upon departure at Purgatory's end, returning to Limbo while Dante ascends toward Heaven with Beatrice.