Argan is a wealthy French aristocrat and severe hypochondriac who wholeheartedly believes he is constantly ill. His daily routine revolves around acquiring and administering medical treatments, sedatives, and purges. As the patriarchal head of his household, he views his family members as tools to serve his needs, attempting to arrange their lives entirely around securing round-the-clock, free medical care for himself.

Béline is Argan's second wife and the stepmother to his two daughters. She outwardly performs the role of an affectionate, devoted spouse who constantly worries about Argan's supposedly failing health. Beneath this loving facade, she actively schemes to secure his entire fortune for herself by consulting a notary and attempting to force her stepdaughters into a convent to remove them from the inheritance.

Angélique is Argan's innocent and beautiful older daughter. She wishes to marry for love and desires a future with Cléante, a young man who gallantly defended her at the theater. Despite her desire for independence and romance, she feels bound by duty to her father, facing the very real threat of being sent to a convent if she refuses his arranged match with a bumbling medical student.

Toinette is the household's headstrong, witty, and clever maid. Emotionally invested in the family, she constantly meddles in their affairs to protect them from themselves. She openly mocks Argan's hypochondria and pretends to ally with Béline in order to secretly work against the stepmother's schemes and assist Angélique in marrying for love.

Louison is Argan's eight-year-old daughter. Caught in the middle of the household's schemes, she attempts to keep her older sister's secrets but is coerced by her father into revealing information about Cléante's visit. Playful and highly dramatic, she feigns death to escape physical punishment.

Béralde is Argan's brother and a voice of reason who attempts to intervene in the household's chaos. He approaches the practice of medicine with deep skepticism, viewing doctors as overblown charlatans who profit off the healthy. He genuinely cares for his brother and nieces, using logical arguments and theatrical entertainment to try and break Argan's costly obsession with medical treatments.

Cléante is a clever and passionate young military swordsman who falls in love with Angélique after defending her from a boorish man at the theater. To bypass Argan's strict control over his daughter, Cléante disguises himself as a substitute music teacher, using improvised musical performances to communicate his true feelings right in front of her family.

Dr. Lillicrap is a physician who relies on archaic theoretical knowledge and pompous language to project authority. He admits to preferring the middle class as patients because they do not expect to actually be cured. As a father, he is blindly proud of his awkward son, twisting Thomas's slow-wittedness into signs of academic perseverance.

Thomas Lillicrap is a newly minted, bumbling doctor who relies entirely on memorized lines and his father's prompting to navigate social interactions. Gawky and obstinate, he staunchly rejects modern medical discoveries in favor of outdated traditions. He views marriage as a strictly one-sided transaction, offering to take Angélique to view a cadaver dissection as a romantic gesture.

Dr. Purgeon is Argan's primary doctor and the uncle of Thomas Lillicrap. He subjects Argan to a constant cycle of unnecessary purges, steadily draining his patient's substantial fortune. His medical practice is driven by an immense ego, leading him to throw a tantrum and formally curse Argan with death when his absolute authority is questioned.

Mr. Florid is an apothecary who works directly as Dr. Purgeon's assistant. He handles the practical, unglamorous side of medicine, mixing and administering the frequent and odiferous purges that his superior prescribes from afar.

Mr. Goodfellow is a notary brought in by Béline to help manipulate Argan's estate. Knowledgeable about Paris inheritance laws and complex legal loopholes, he assists in finding roundabout ways for Argan to bypass restrictions and transfer his wealth directly to his wife.

Punchinello is an older moneylender and Toinette's former lover who appears during the play's musical interludes. Consumed by what he calls the disease of love, his romantic serenading attempts are continually interrupted by mocking locals, musicians, and corrupt constables who extort him.