Nene is a 27-year-old gay Puerto Rican man working as a sex worker. He previously spent time in a psychiatric hospital as a teenager for experiencing dissociative episodes called blackouts, where he first met Juan. He describes himself as a chronic loser and currently acts as a caretaker and listener for his dying friend, spending his days and nights in a blending routine.

Juan is an elderly gay Puerto Rican man nearing the end of his life. As a child, he modeled for a children's book illustrator and was briefly adopted by a lesbian couple before spending large portions of his life institutionalized for a culture-bound diagnosis of Puerto Rican Syndrome. He possesses a deep, encyclopedic knowledge of queer history and literature, dedicating his remaining time to safekeeping this information.

Born Helen Reitman, Jan is a real-life lesbian sexologist and researcher from the 1920s and 1930s. She gathers interviews from lesbian women in Europe and New York, providing the foundational research for the Sex Variants study. She continuously battles male medical professionals who seek to co-opt her work and label queer identity as a disease.

Liam is Nene's long-term ex-boyfriend. The two men met and worked together as farmhands in Virginia in their early twenties, eventually protesting the World Bank. He struggles with the financial realities of holding down two jobs and reacts explosively when discovering Nene's ongoing sex work.

Norwood is an older white man who hires younger men for sex work. He lives in a predominantly white town and asks his clients to wear diapers during their encounters. He keeps his private life and sexual preferences hidden from the broader community while projecting a polite, somewhat controlling demeanor.

Born Eleanor Byrnes, Zhenya is a children's book author and illustrator. She creates books featuring animals and young boys, specifically using young Juan as her muse for a character named Manuelito. She informally marries Jan and briefly helps raise Juan before sending him to live with relatives in Spanish Harlem.

Dr. Henry is a medical professional who takes over the Committee for the Study of Sex Variants. He ultimately publishes the research with an anti-queer conclusion, determining that gay and lesbian people are socially maladjusted. He controls which participants' stories are included in the final publication, favoring clinical pathology over human emotion.

Thomas, or Thom, is an amateur researcher born to a wealthy family but disinherited upon coming out as gay. He recruits participants for the Sex Variants study and keeps personal notes on his own sexual encounters. He later visits Puerto Rico to conduct sociological studies.

Ben Reitman is an American gynecologist who attends to patients who cannot afford medical care. He is known as a hobo folk hero and anarchist, but he abandons his wife and daughter when Jan is an infant. His notoriety and political activism heavily influence Jan's worldview, despite her resentment toward him.

Sal is a 19-year-old fictionalized analogue for Nene. He engages in sex work with older white men, including Norwood, and lives in a small town where he hangs out with a group of white female friends he calls the girls. He projects an aura of victimization while harboring deep desires for protection.

Dr. Dickinson is a medical professional who studies the gynecology of homosexuality. Although he lacks the intense moral judgment of some of his peers, he still considers lesbianism a disease to be cured through anatomical study. He flatters Jan into helping him recruit subjects from the underground queer community for his research.

Nene's father is a Puerto Rican former Air Force member who later becomes a state trooper assigned to narcotics. He forces his family to move to North Dakota after converting to be a Jehovah's Witness. He is physically volatile toward his wife and children, adopting a tough persona for his police work.

Nene's mother is a white woman from Brooklyn who was sent to a home for unmarried mothers before marrying Nene's father. She endures severe domestic violence but initially refuses to press charges. She is described by Nene as a screamer but is fiercely protective of her children when aided by others.

Emma Goldman is a famous anarchist speaker and activist. She engages in an affair with Ben Reitman, who acts as her manager, and their political notoriety deeply influences young Jan Gay from afar.

Oma is Jan's grandmother. She provides physical and emotional care for young Jan when her mother panics, and she actively criticizes Ben Reitman for bringing tension into their household.

Franziska is a dancer and civil rights pioneer who pioneers dance therapy. She is Jan's lover and allows Jan to live in her dance studio loft, creating a safe space for various artists and creatives.

Salvatore is a participant in the Sex Variants study. He genuinely seeks help for heartbreak over a dockworker, but he finds himself pressured by the medical establishment to focus strictly on clinical sexual details rather than his emotions.