Frances is a dedicated social worker and economist who moves to Hell's Kitchen to study childhood poverty. She is fiercely determined to enact meaningful labor reform and social insurance. Balancing a demanding public career with a complicated private life, she demonstrates immense political acumen while refusing to compromise her core moral vision.

Franklin is a charismatic and ambitious politician who rises from a state senator to the President of the United States. Initially appearing arrogant and dismissive of labor reforms, he matures into a pragmatic leader, especially after his struggle with polio. He serves as both a gatekeeper to power and an essential partner in Frances's reform efforts.

Paul is a well-dressed, charming progressive Republican who courts Frances and promises her a modern marriage that accommodates her career. He possesses a brilliant analytical mind but struggles with severe bouts of bipolar disorder and depression, requiring significant care and altering the trajectory of their family life.

Mary is a wealthy debutante with a railroad baron father who leverages her privilege to support social reform. She becomes Frances's most trusted confidante, roommate, and political bridge. She uses her high-society connections to facilitate important legislative goals and provides a steady support system for Frances's family.

Susanna is the only surviving child of Frances and Paul. She grows up in the shadow of her mother's high-profile political career and her father's severe illness. She possesses a keen mind and an interest in the arts, but struggles with the pressures of her family's unique situation and the frequent absences of her parents.

Florence is a legendary social reformer and intense, uncompromising advocate for workers' rights. She serves as an idol and mentor to Frances, teaching her the vital tactics of investigating, agitating, and legislating. She routinely pushes Frances to ignore restrictive expectations of polite behavior to achieve real political victories.

Al is a prominent New York politician and product of the Tammany Hall machine who rises to become the Governor of New York. He is a practical dealmaker who genuinely cares about the working class. He recognizes Frances's talent early on, pulling her into government service and championing her expertise despite her gender.

Eleanor is the niece of Theodore Roosevelt and later the First Lady of the United States. She is a frank, politically active woman who shares Frances's progressive ideals. They bond over the shared, hidden burdens of their husbands' respective illnesses, though Frances sometimes observes the distance created by Eleanor's immense wealth and privilege.

Sinclair is a talented but eccentric writer and reporter who aggressively pursues Frances romantically in their youth. Though Frances rebuffs his advances, he remains a fixture in her life. He often views her political dedication with a mix of admiration and skepticism, eventually writing novels that draw uncomfortably from their shared history.

Charlie is a bright, young lawyer from Boston whom Frances appoints as the Solicitor of Labor. He proves to be a vital ally, helping her draft major legislation and find creative legal loopholes, such as authorizing bonds to allow Jewish refugees to escape Nazi Germany and enter the United States.

Known as "Iron Pants," Hugh is a former brigadier general and a combative figure within the Roosevelt administration. He frequently clashes with Frances over economic policy and labor rights, preferring authoritarian, business-friendly approaches that directly conflict with Frances's progressive New Deal goals.

Miss Mathews is the severe supervisor of the Hartley House settlement in Hell's Kitchen. She embodies the traditional, conservative approach to charity work, enforcing strict rules against giving direct aid to the poor and expressing deep skepticism about a woman pursuing an advanced degree in economics.

Thomas is a political boss associated with the Tammany Hall machine in New York City. Despite his rough exterior and connection to machine politics, he proves surprisingly helpful to Frances on multiple occasions, demonstrating how practical relationships yield direct results for those in need.

John is the Mayor of New York City who frequently uses Frances and Paul's home as a respite from the stresses of his office. He relies heavily on Paul's financial expertise to manage the city's budget before the outbreak of World War I changes his trajectory.

Belle is a highly capable political strategist who works closely with Al Smith. She is fiercely loyal to Al and frequently views Franklin D. Roosevelt with suspicion, causing friction when Frances attempts to manage the divide between the two political figures.