In the film the protagonist is an artist compelled to paint this image by a force he doesn't comprehend.
Here is a excerpt from Dante's Inferno's wiki and an accompanying image for illustrative purposes.
In the very centre of Hell, condemned for committing the ultimate sin (personal treachery against God), is the
Devil, referred to by Virgil as
Dis (the Roman god of the underworld; the name "Dis" was often used for
Pluto in antiquity, such as in Virgil's
Aeneid). The arch-traitor,
Lucifer was once held by God to be fairest of the angels before pride caused his rebellion against God and resulted in his expulsion from Heaven. Lucifer is a giant, terrifying beast trapped waist-deep in the ice, fixed and suffering.
He has three faces, each a different color: one red (the middle), one a pale yellow (the right), and one black (the left):
... he had three faces: one in front bloodred;
and then another two that, just above
the midpoint of each shoulder, joined the first;
and at the crown, all three were reattached;
the right looked somewhat yellow, somewhat white;
the left in its appearance was like those
who come from where the Nile, descending, flows.
[104]
Dorothy L. Sayers notes that Satan's three faces are thought by some to suggest his control over the three
human races: red for the Europeans (from
Japheth), yellow for the Asiatic (from
Shem), and black for the African (the race of
Ham).
[105] All interpretations recognize that the three faces represent a fundamental perversion of the
Trinity: Satan is impotent, ignorant, and full of hate, in contrast to the
all-powerful,
all-knowing, and
all-loving nature of God.
[105] Lucifer retains his six wings (he originally belonged to the angelic order of
Seraphim, described in
Isaiah 6:2), but these are now dark,
bat-like, and futile: the icy wind that emanates from the beating of Lucifer's wings only further ensures his own imprisonment in the frozen lake.
He weeps from his six eyes, and his tears mix with bloody froth and pus as they pour down his three chins. Each face has a mouth that chews eternally on a prominent traitor. Marcus Junius Brutus and
Gaius Cassius Longinus dangle with their feet in the left and right mouths, respectively, for their involvement in the
assassination of Julius Caesar (March 15, 44 BC) – an act which, to Dante, represented the destruction of a unified Italy and the killing of the man who was divinely appointed to govern the world.
[105] In the central, most vicious mouth is
Judas Iscariot, the
apostle who betrayed Christ. Judas is receiving the most horrifying torture of the three traitors: his head is gnawed inside Lucifer's mouth while his back is forever flayed and shredded by Lucifer's claws. According to Dorothy L. Sayers, "just as Judas figures treason against God, so Brutus and Cassius figure treason against Man-in-Society; or we may say that we have here the images of treason against the Divine and the Secular government of the world."
[105]
https://en.wikipedia.org/wiki/Inferno_(Dante)