Arkady has recently graduated from a school in St. Petersburg. While a student, he has become fascinated with a new philosophy called nihilism. Nihilism is the belief in nothing. Arkady still loves his father, but he is easily influenced by others. The ideas that he picks up at the university are very different from his father's ideas. He thinks of himself as modern and sophisticated.
Bazarov becomes friends with Arkady while a medical student at the University of St. Petersburg. It is Bazarov who introduces his new friend to nihilism and other radical ideas. He has an intoxicating personality, and is very convincing when he speaks. He likes to argue and prove others wrong. He has a very high opinion of himself, and this gets him into trouble.
Nikolai is Arkady's father, and he doesn't understand what has happened to his son while he was away at school. He feels completely left behind and out of touch. He cares for his son and is welcoming to his new friend Bazarov, but they make him feel awkward. Nikolai is a simple farmer, and Bazarov and Arkady's conversations go over his head.
Pavel is Nikolai's brother. He is angry with the young men Arkady and Bazarov because of the new ideas they bring from the city. Mostly he is angry with Bazarov because the young man is so arrogant. They get into lots of arguments. At one point, they even have a duel, in which Pavel is injured. Unlike his brother, Pavel won't tolerate the bad manners of the young men, especially Bazarov.
Odintsova is a widow with a lot of money. She also has very modern ideas, like the young men. Bazarov is in love with her, but Odintsova does not return the feelings. She is intellectual but not passionate. She is like a female version of Bazarov.
Katya is Odintsova's younger sister. She is much more down to earth than Odintsova. She is kind and generous. She develops feelings for Arkady almost as soon as she meets him. At first, Arkady doesn't notice Katya's affection. Eventually, he develops feelings of his own. Near the end of the novel, Katya and Arkady get engaged and then start a family.