Johann Wolfgang von Goethe published Faust in 1808, nearly a century before Leroux wrote The Phantom of the Opera. Goethe's Faust is the story of a scholar who sells his soul to the devil in exchange for worldly pleasures and knowledge. The story is loosely based on the life of Johann Faust, an alchemist and necromancer. Charles Gounod wrote Faust (the opera), which premiered in 1859.
Leroux's The Phantom of the Opera frequently references both the original story and the opera; Christine sings the role of Marguerite and faints onstage. In Chapter 8, the narrator describes an encounter with the Phantom during a performance of Faust:
The famous tenor Carolus Fonta had barely launched into Doctor Faust’s first appeal to the powers of darkness, when Firmin Richard, who was sitting in the ghost’s own chair – the chair at the front on the right – leaned over to his partner and enquired cheerily: "Tell me, has the ghost whispered a word in your ear yet?"
"Faust" means "auspicious" or "lucky" in Latin, but here the performers are anything but lucky; in this scene, the director Moncharmin refers to the opera house as "a house with a curse upon it." They anticipate the Phantom's arrival during the middle of the first act. Carolus's performance seems like a mere appropriation of the story over which the Phantom obsesses; her voice could never match his or Christine's.
Tangentially, Erik becomes obsessed with the female love interest in the tale of Faust. The story's protagonist is promised the love of the most beautiful woman in the world; likewise, Erik hopes to be loved by Christine. The character Faust represented the mind and soul of the Romantic era; he exemplified self-consciousness and a crisis of identity very similar to the one that Erik experiences due to his separation from society.
Don Juan is a fictional character who first appeared in 1630 in the tragic drama El burlador de Sevilla ("The Trickster of Seville") by Tirso de Molina. In this tragedy, Don Juan seduces a noble girl and kills her father. Much to his surprise, the father's ghost returns as a harbinger of Don Juan's death. In 1787, Mozart wrote an opera called Don Giovanni, which secured the story's place in modern film and media.
In Leroux's The Phantom of the Opera, Erik aspires to write his own opera titled Don Juan triumphant. This is significant because Don Juan's story resembles the forbidden, mostly one-sided romance between the Phantom and Christine. In Chapter 13, Erik says of his music:
My Don Juan has not been composed to a libretto by Lorenzo Da Ponte, nor inspired by wine, wanton love and profligacy doomed to incur the wrath of God. If you like, I can play you Mozart’s version, so that you may shed your beautiful tears and indulge in pious thoughts. You see, Christine, my own Don Juan is not carried off to Hell by demons, and yet he burns …
Here, Erik references Don Juan's appearance in operas by Lorenzo Da Ponte and Mozart. He insists that his Don Juan "burns" in a different way (perhaps with passionate love). Much like Don Juan, Erik's attractive qualities—such as his musical talent and his capacity for love— heighten the dramatic value of his ultimately tragic end.
After Carlotta's fatal performance, Christine begs the Phantom to reveal himself to her. She fears that he was killed by the falling chandelier and desires to know if he is still alive. The name Lazarus appears in Chapter 13 in her plea as an allusive metaphor:
The Voice did not reply, but suddenly I heard a long, exquisite lament, which I knew well. It was the plaint of Lazarus when, at the sound of Jesus’ voice, he begins to open his eyes and see the light of day. It was my father’s violin weeping; I even recognized his bowing stroke. It was the sound that made us, you and me, stop in our tracks as children – the sound that cast its spell over the graveyard that night at Perros. The invisible, triumphant violin played again the joyous cry of Life and at long last I heard the overwhelming, sovereign call of the Voice singing the words: “Come! And believe in me! He that believeth in me, though he were dead, yet shall he live!"
The quote within the quote above ("He that believeth in me...") is from the Gospel of John where it's spoken by Jesus just before the raising of Lazarus, and the words "sovereign call" suggest that the sung quote identifies the Phantom's voice with that of Jesus.
In addition to the biblical figure Lazarus, the novel also refers to the piece Lazarus that Christine's father used to play. According to the Bible, Lazarus rose from the dead; and the song her father played symbolized the potential for hope and redemption. This allusion suggests that the Phantom, like Lazarus, is still alive, and Christine is relieved and frightened by this thought at the same time.