Who is the three-faced monster at the bottom of Hell?

The three-faced monster at the bottom of Hell is Lucifer.

In Dante’s Inferno, Lucifer is trapped waist-deep in the frozen lake Cocytus at the very center of the Ninth Circle, where the worst traitors are punished. He is enormous, winged, and immobilized by the icy wind produced by his own beating wings.

Lucifer’s three faces are a grotesque parody of the Christian Trinity. Each face has a mouth, and each mouth eternally chews one of the three great traitors: Judas Iscariot, Brutus, and Cassius. The figure is often called Satan as well, but Lucifer is the name used for the fallen angel in Dante’s description.

A common mix-up is Cerberus, the three-headed watchdog of the Third Circle, who torments the gluttonous. Lucifer is not a guardian stationed at Hell’s entrance; he is the imprisoned ruler-like figure at its deepest point.