resides at the bottom of Hell's ninth and final circle, known as the frozen lake of Cocytus. 

Lucifer's three faces symbolize his twisted nature and his rebellion against God. He is portrayed as the ultimate embodiment of evil and betrayal, eternally punishing the souls of history's greatest traitors, Judas Iscariot, Cassius, and Brutus, by endlessly chewing on them with his three mouths.

Oh what a sight!

How passing strange it seem'd, when I did spy

Upon his head three faces: one in front

Of hue vermilion, th' other two with this

Midway each shoulder join'd and at the crest;

...At every mouth his teeth a sinner champ'd

Bruis'd as with pond'rous engine, so that three

Were in this guise tormented.

Piccarda

In Paradiso, Dante encounters Piccarda in the sphere of the Moon, representing the souls unfaithful to their vows, particularly the vows of chastity. Piccarda was a nun who was forced to leave her convent and marry against her will due to the political machinations of her family. 

Although she could not fulfill her religious vows, Piccarda's soul resides in Heaven because she remained faithful to God in her heart and accepted her fate with humility and resignation. In the celestial realm, the souls are perfectly content with their place in the divine order, and Piccarda's humility and acceptance are emblematic of this state of bliss.

...but thou wilt know

Piccarda, in the tardiest sphere thus plac'd,

Here' mid these other blessed also blest

...She with those other spirits gently smil'd,

Then answer'd with such gladness, that she seem'd

With love's first flame to glow: "Brother! our will

Is in composure settled by the power

Of charity, who makes us will alone

What we possess, and nought beyond desire;"

Piccarda Donati was also an actual historical figure, a member of the noble Donati family in Florence during Dante's time.

Beatrice

Beatrice summons Virgil from limbo (Inferno 2) to lead Dante through hell, up the Mount of Purgatory to the Garden of Eden. She sits with the blessed in the heavenly rose, where she waits to replace Virgil as Dante’s guide (Purgatory 30). Beatrice, “bringer of blessedness,” is therefore largely responsible for Dante’s salvation. The historical Beatrice Portinari (1266–90) was the daughter of Folco Portinari, a wealthy Florentine, and his wife, Simone dei Bardi. In his Vita Nuova (New Life), Dante claims to have met and fallen in love with her when they were about nine years old. The Vita Nuova consists of love poems Dante wrote to Beatrice, which he connected with prose commentaries. The physical love he had for her, which is the subject of the Vita Nuova, was transformed into the spiritual love that enabled his salvation, which is the subject of The Divine Comedy.

Dante

Dante the character is Dante the poet’s alter ego, a kind of “Everyman” (someone whom everyone can relate to) whose travels the reader follows, experiencing the three regions while he does. Ideally, as Dante learns from his encounters with countless shades, the reader attains, along with him, a degree of enlightenment. Virgil, author of The Aeneid, traditionally seen as the voice of reason, leads Dante through hell and purgatory, where Dante learns about the nature of sin in all its guises. Through Virgil’s instruction, which is sometimes imperfect, Dante learns, most importantly, not to pity sinners but to have compassion for them, not to hate the sinner but the sin. Virgil takes Dante to the Garden of Eden at the top of the Mountain of Purgatory, where Matilda becomes their guide (Purgatory 28). She leads them through the garden and gives way to Beatrice (Purgatory 30), who takes Dante the rest of the way through purgatory and up into heaven. There Saint Bernard (Paradise 31) replaces her and guides Dante until he is able to travel on his own.

Dante the poet and Dante the character are not the same, at least not until the final few lines of the poem. Dante the poet tells us that he actually made this journey to God and was told to return to earth and write what he saw. Like his alter ego, the poet was naive and unschooled when he entered hell’s mouth. He returns to his earthly life a wiser person, secure in the knowledge that there is a place reserved for him in heaven (which he will occupy after spending time in purgatory for being prideful). Only after Dante the character makes the journey and attains the poet’s wisdom through experience, only after he meets God face to face in Paradise, do the poet and character merge. There, for a brief moment, the poem’s past tense shifts to the present, to Dante’s Florence, where the two become one, as the poet writes the character’s vision of God and his recounting that vision.

Ulysses

Ulysses is the crafty hero of Homer’s epic Greek poem TheOdyssey. Ulysses is the son of Laertes, King of Ithaca, and father of Telemachus. Homer’s poem tells the tale of his wandering for twenty years after the Trojan War and of his return to Ithaca. Dante created the events he tells about Ulysses and his crew and places him in hell with his Greek warrior companion, Diomed (Inferno 26). There he has the proud Ulysses tell of how he disobeyed Hercules’s instructions and convinced his men to sail beyond the Pillars of Hercules and the bounds of the known world. He explains how they sailed into the southern hemisphere, where they saw Dante’s Mount of Purgatory just before their ship was pulled beneath the waves where they all perished. Dante uses the story as a contrast to his own, which was divinely sanctioned.

Virgil

Publius Vergilius Maro (70–19 BCE) was one of the greatest Roman poets and is Dante the character’s guide through hell and most of purgatory. Virgil’s Aeneid tells the story of Aeneas’s founding of Rome after the Trojan War and was a major inspiration for Dante’s Divine Comedy. In the famous book 6 of The Aeneid, the pagan Aeneas travels to the underworld, where he sees the wicked suffering and the virtuous living a life of comfort and ease. This episode provided Dante, along with other literary accounts of underworld journeys, with the basic structure for his vision of the Christian hell. During the Middle Ages, Virgil had a reputation as a magician and wizard. Saint Augustine, the emperor Constantine, and others thought Virgil’s Fourth Eclogue prophesied Christ’s birth. Dante and Virgil encounter the Roman poet Statius (45–96) on the Mountain of Purgatory (Purgatory 21), where Statius claims that Virgil's Fourth Eclogue was responsible for his conversion to Christianity.

Virgil’s Aeneid was the basic Latin textbook in medieval schools. Students learned grammar, rhetoric, and the language by translating Virgil’s Latin. Dante would have been no exception. Since Latin was the language of the literate in the Middle Ages and since most people learned it from Virgil, his Aeneid was one of the most well-known books. It is still used in many Latin courses today.