In my opinion, the Phantom is the antagonist of Phantom of the Opera.
He is a very mysterious and dark character. He is a troubled man with a very tragic and horrible past. He has been judged his entire life for his deformed face and was never shown love or compassion growing up. He is ashamed of his face so he hides it by wearing the mask. He falls in love with Christine, but that love falls unrequited, but he doesn’t deal with it well. He responds to his entire situation in revenge and in destructive ways. He wants everything to go his way. He wants Christine to be the star and tricks her by pretending to be her “angel of music”.
Phantom manipulatives Christine on multiple occasions. He threatens the Opera House. He causes the chandelier to fall during a performance. So he does many destructive things during the course of the show. When Christine falls in love with Raoul, he feels betrayed and seeks even more revenge, and he plans to kill Raoul and wants Christine all to himself. In the final lair scene, he makes Christine choose between having him kill Raoul or staying with him. But through an act of compassion shown by Christine, he finally lets them go. Christine kisses him and that allows Phantom to let him go. The Phantom does not know how to handle situations well and cannot accept his deformed face and has led a very tragic life.