Dr. Heidegger: He is a mysterious character. Dr. Heidegger is a doctor, but he is also a philosopher interested in moral questions. We learn that he has many secrets, and that several of his patients have ended up dead. We also do not know the reasons for him to run this experiment.
The widow Wycherly: The widow is a woman who was beautiful before, but ruined her reputation because of her relationships with men. She is vain, loves attention and tries to entice men.
Mr. Medbourne: He is a greedy character who lost his fortune due to his ambition and his risky investments. He is obsessed with money and success.
Colonel Killigrew: The Colonel is a hedonist. He likes excess and pleasure, and he squandered his money pursuing this.
Mr. Gascoigne: Mr. Gascoigne's obsession is power. An ex-politician, he likes to control and command. His ideologies and opinions are unclear, but we learn that he desires power for power's sake.
