There are a lot of important characters in the Phantom of the Opera, so I will try to list them all:

• The Phantom of the Opera (aka Erik, the Opera Ghost, and the Angel of Music): titular character, lives beneath the opera house, falls in love with Christine as he teaches her to sing.
• Christine Daae: daughter of a famous Swedish violinist, a soprano singer at the opera, the Phantom falls in love with her.
• Raoul (the Vicomte de Chagny): Christine's friend from her youth, new patron of the opera, Christine's other love interest (and the eventual winner).
• Philippe (the Comte de Chagny): Raoul's brother.
• Armand Moncharmin and Firmin Richard: the new owners of the opera.
• Madame Giry: looks after the patrons who sit in the boxes, serves as a sort of liaison between the Phantom and the others in the opera.
• Meg Giry: Madame Giry's daughter and a dancer in the ballet.
• The Persian: a friend from the Phantom's past.
• La Carlotta: the lead soprano at the opera, Christine's predecessor.
• Joseph Bouquet: works backstage, provides first description of the Phantom, hanged by the Phantom.
• Debienne and Poligny: the previous owners of the opera.
• Madame Valerius: Christine's guardian after the death of her father.

There are other minor characters, but these are the ones who are most important to the story.