Court composer to the Emperor of Austria, Salieri is "the most successful young musician in the city of musicians," yet he is also consumed with envy of Mozart's prodigious musical talents. He finds himself mediocre by comparison. Providing a brief portrait of his background, he explains that his parents were

. . . provincial subjects of the Austrian Empire. . . . Their notion of God was a superior Habsburg emperor. All they required of Him was to protect commerce, and keep them forever preserved in mediocrity. My own requirements were very different. I wanted 'Fame'. . . . Yet only in one especial way. Music! Absolute music. . . . Already when I was ten a spray of sounded notes would make me dizzy almost to falling. By twelve, I was stumbling about under the poplar trees humming my arias and anthems to the Lord. My one desire was to join all the composers who had celebrated His glory through the long Italian past.

When Mozart's talents clearly surpass his own, he feels as if God is mocking him. As a result, Salieri declares war against God "through His preferred Creature—Mozart . . . in the waging of which, of course, the Creature had to be destroyed.'' Salieri eventually contributes to Mozart's destruction, yet admits that he did not escape God's punishment. He had fame, but it was for what he knew to be "absolutely worthless."

Salieri, however, is tenacious. He decides, "I did not live on earth to be His joke for eternity. I will be remembered . . . if not in fame, then infamy." When he falsely confesses to poisoning Mozart, he insists "for the rest of time whenever men say Mozart with love, they will say Salieri with loathing. . . . I am going to be immortal after all." Yet he is again thwarted. His suicide attempt fails, and no one believes his confession. At the end of the play, he is enveloped in his bitterness as he addresses the audience as the "Patron Saint of Mediocrities."

We see Mozart through Salieri's memory. Salieri does provide some background information on the famous prodigy. He wrote his first symphony at five, his first concerto at four, a full opera at fourteen, and is twenty-five when Salieri meets him. The stage directions introduce him as "a small, pallid, large-eyed man in a showy wig and a showy set of clothes." Mozart is "an extremely restless man, his hands and feet in almost continuous motion, his voice is light and high, and he is possessed of an unforgettable giggle—piercing and infantile." He enjoys ribaldjokes and bathroom humor, a quality which disgusts and angers Salien, who insists his own virtuous nature deserves to be blessed by God.

Mozart has a love/hate relationship with his father, whom he fears but also respects. He desperately needs his father's approval and so reincarnates him in his compositions. The venticelli tell Salieri that Mozart is "wildly extravagant" and lives way beyond his means. His outbursts in public have become "embarrassing " He "makes scenes" and thus often "makes enemies." Yet, Salieri insists that God has chosen him as his voice, as evident in his exquisite music. Mozart comments on his role as artist and his goal to make

a sound entirely new. . . . I bet you that's how God hears the world. Millions of sounds ascending at once and mixing in His ear to become an unending music, unimaginable to us. That's our job . . . we composers, to combine the inner minds of him and him and her and her—the thoughts of chambermaids and court composers—and turn the audience into God.

By the end of the play,...

Constanze Weber, who later becomes Constanze Mozart, is the daughter of Mozart’s landlady and eventually his wife. She is characterized as well-meaning and innocent, yet she mirrors Mozart’s coarseness and eccentricities. Although she remains devoted to her husband, Constanze inadvertently creates a rift between him and his father, Leopold, leading to a strained relationship until Leopold’s death in Salzburg. In times of financial desperation, Constanze approaches Salieri to sell Mozart's compositions to support her struggling family. Despite her growing suspicion of Salieri’s true intentions, she is unable to prevent Mozart’s downfall. After his death, she retires to Salzburg, becoming the "Keeper of his Shrine," symbolizing a bastion of virtue and remembrance.

Joseph II, the emperor of Austria and brother to Marie Antoinette, is depicted as Mozart’s patron who, despite his genuine love for music, lacks the intellectual capacity to fully appreciate Mozart’s genius. His mediocrity and susceptibility to influence by Salieri and other court figures result in consistent hindrances to Mozart’s career. Joseph appoints Mozart as Gluck's successor, albeit at a significantly reduced salary, and often favors Salieri’s compositions over those of Mozart.

Baron Gottfried Van Swieten (GOT-freed fan SWEE-tehn) is the meticulous prefect of the Imperial Library and a staunch Freemason, affectionately nicknamed "Lord Fugue" due to his traditional musical tastes. He plays a supportive role in Mozart’s life following Mozart's initiation into the Freemason brotherhood. However, Van Swieten becomes estranged from Mozart after the composer incorporates Masonic rituals into The Magic Flute, a move suggested by Salieri. Feeling betrayed, Van Swieten withdraws his support, arranging only for a pauper's funeral for Mozart and ensuring his burial in an unmarked grave.

The “Venticelli” (VEHN-tee-CHEH-lee), also known as the "Little Winds," fulfill the role of the play's chorus, responsible for disseminating gossip and rumor. Their rapid-fire dialogue echoes the urgency and chaos of the information they share, providing Salieri—and the audience—with insights into the dramatic events unfolding. Their contributions underscore the chaotic atmosphere of the court and highlight Salieri’s dependence on hearsay to maneuver through the web of courtly intrigue.

Though never appearing on stage, Leopold Mozart exerts a formidable influence as Wolfgang’s father. Salieri describes him as "a bad-tempered Salzburg musician," highlighting the complex relationship between Leopold and his son. Despite their tense interactions, Leopold’s death has a profound impact on Wolfgang, plunging him into despair. His stern paternal image is captured in Don Giovanni and later softened in The Magic Flute, where he is portrayed as a benevolent figure.

Katherina Cavalieri, initially a silent figure in the narrative, is Salieri’s pupil and becomes enmeshed in affairs with both Salieri and Mozart. Her role evolves as Salieri, feeling betrayed by God, takes her as his mistress. By the conclusion of the play, Katherina undergoes a transformation, depicted as "fat and feathered like the great song-bird she'd become," signifying her personal growth and the passage of time.

Count Franz Orsini-Rosenberg, head of the Imperial Opera, is an ardent supporter of the Italian faction at court. He holds a critical stance towards non-Italian opera, often dismissing Mozart’s compositions as excessive, citing "too many notes." His deep-seated prejudice against prodigies like Mozart illustrates his resistance to change and innovation in the arts.

Count Johann von Strack (YOH-hahn fon SHTRAK), the royal chamberlain, acts as a formal and rigid advisor on musical matters. He is entrusted with delivering the emperor’s commission for Mozart to compose a German comic opera, an action that further alienates the Italian faction at court.