Robust, energetic, and, as Cusins suggests, the incarnation of loveliness, Barbara is the play's savior. She begins the play as a major for the Salvation Army who is peacefully convinced of her mission to redeem mankind through Christian dogma. Her father's arrival forces her to reevaluate her beliefs. The demonstration of his power over the Army will force her to realize that the wealthy, rather than God, hold the world and its salvation in their hands. Utterly disillusioned, she sheds her uniform and abandons her work. Her Father has forsaken her, leaving Undershaft in His place.
Soon thereafter, however, Barbara's visit to Undershaft's ideal community of Perivale St. Andrews will lead her to recognize the armory as necessary to man's redemption, bloodshed necessary to salvation, evil necessary to good. For Barbara, "life is all one," and she can return to the Army with her new father's gospel in mind. As in most conversion narratives, Barbara's epiphany demands a death—thus "Major Barbara will die with the colors"—and her rebirth. She ends the play by regressing to girlhood, calling for her mother, tugging at her skirts, and asking her to help choose her new house in the planned community.
As Undershaft insists, Barbara's own "inspiration," rather than the truth of Christianity, makes her man's savior. The daughter of a foundling, Barbara ostensibly lacks social class and comes "straight from the heart of the whole people." She considers herself universal, a woman who can serve as savior to everyone. Perhaps this universality explains why Shaw does not particularly describe her in the stage notes. Ironically, Barbara's proclamation would blatantly deny the class status that makes her Salvationist career possible. As revealed by her assault on Bill Walker in Act II, Barbara is not only compelling because of the "inspiration" she exudes, but also the authority she wields in her aristocratic heritage, polished speech, and professional manner.
The great arms industrialist of Europe, Undershaft returns to his long abandoned family with to wreak havoc, like Mephistopheles, with a new gospel of society's redemption. He is a man of "formidable reserves of power, both bodily and mental, in his capacious chest and long head." His gentleness is that of a "strong man who has learnt by experience that his natural grip hurts ordinary people."
Undershaft understands himself in participating in a greater power that controls the world—not the Salvation Army of God, but the armory proper. The Undershaft firm represents an alternative canon of sorts, charting a long tradition of Saint Andrews who have quietly held Europe under their thumbs and determined the course of history.
Like Cusins, he is bent on winning Barbara, though more for his cause than love. He recognizes an inspiration in her that—as with himself and Cusins—elevates her above the common herd. The three of them must band together to determine the course of society.
As with his predecessors, Undershaft is a foundling who understands himself as having established himself in the world through the force of his will alone. This will has committed him to an agonistic struggle with others. As Undershaft proclaims, a sacred commandment—"Thou shalt starve ere I starve"—set him on the path from poverty to greatness. Through the murderous struggle with others, Undershaft has realized his will. Thus his "bravest enemy" is his best friend, a rival who keeps him "up to the mark." Over and against Christian ideals of human brotherhood, the recognition Undershaft demands from his neighbor is not love but obedience and respect, a bending to his will. Again, the struggle he stages with others is decidedly violent: those who do not submit to his desire must die.
Cast as the poet within the play's triumvirate of madmen, Cusins is a "slight, thin haired, and sweet voiced" Greek scholar determined to marry Barbara at all costs. As Shaw notes, it is not love that drives him to Barbara but an unmerciful "instinct." He joins the Salvation Army as a result but, as Undershaft remarks, the hollowness of his Army drum symbolizes the hollowness of his conviction in the organization. Indeed, Cusins uses the Army much like he does his drum, considering it an instrument for his Dionysian ecstasies. Understanding himself as a "collector of religions," he does not subscribe to any particular "pathfinder of salvation," but seeks only that which brings reality, power, and jubilation to the people. A student of the great democrat Euripides, he clings above all to a belief in this love for the people.
Upon Undershaft's attempt to convert him to his gospel, Cusins is particularly seduced by what he describes as his Mephistophelean "ecstasy of mischief." By "mischief" Cusins refers to his calculated sense of irony and wily argumentation in securing demonstrating to Barbara how he holds the Salvation Army and all its guests in his power. He alone perceives this irony as Undershaft adopts him as a sort of coeval in the previous scene.
This demonstration gives Cusins over to Undershaft's cause. As he cries joyfully, the spirit of "Dionysus-Undershaft" possesses him entirely. Ultimately Cusins will become his successor, shedding his name to assume that of the firm. Unlike Andrew, however, Cusins takes over the armory in the name of his love for the people. He declares that through the armory, he will abandon his bookish studies, work that only served to arm the intellectual against the commoner, and make power for the masses. For Cusins, gunpowder is a power accessible to the common people and that forces the "intellectual oligarchy" to exert itself for the general good.
Shaw describes Cusins as a "determined, tenacious, intolerant person" who presents himself as he is: "considerate, gentle, explanatory, even mild and apologetic, capable possibly of murder, but not of cruelty or coarseness." The "lifelong struggle of a benevolent temperament and high conscience against impulses of inhuman ridicule" has wrecked his constitution.