Doctor Pascal

Doctor Pascal is the protagonist of the novel. He is a medical doctor who spent twelve years practicing medicine and then decided to dedicate the rest of his life to researching and attempting to cure certain conditions. This led him to focus on researching heredity and compiling information about his family, studies which he keeps on files in his study. Doctor Pascal does not wish to become rich or famous from his research and profession but is instead interested in providing healthcare to those who do not have access to it for financial reasons.

Martine

Martine is the housekeeper who has been working for Doctor Pascal for thirty years. While she faithfully works for him, she also greatly disapproves of his non-religious lifestyle. She continually attempts to convert him to Christianity as well as to stop him from continuing his scientific research.

Clotilde

Clotilde is the niece of Doctor Pascal. When Dr. Pascal's brother lost his wife, he sent Clotilde to live with Doctor Pascal. Martine raises Clotilde in a strict Christian manner. Doctor Pascal attempts to intervene with his nonreligious perspective, but, because Martine was much more involved in Clotilde's upbringing, she is successful in raising her to be a devout Christian. Martine and Clotilde are determined to bring Doctor Pascal to church services.

Madame Rougon

Madame Rougon is the elderly mother of Doctor Pascal. She greatly disapproves of his research and the fact that he is not interested in becoming rich or famous. She only sees value in his research if he can use it to cure famous people. She sees no worth in him helping the poor and worries about the life trajectory of her son.

Doctor Ramond

Doctor Ramond is a friend of Doctor Pascal. He is in love with Clotilde and desires to marry her. While Clotilde does consider his proposal, she ends up realizing that she is in love with Doctor Pascal.