There are two major characters featured in "The Bet": the lawyer and the banker, neither of which have official names in Chekhov's short story.
The lawyer is seen to be persistent, intelligent and self-motivating. He does not break down in the 15 years of imprisonment as the banker foretold. He is intelligent by the virtue of reading so many books, which reflects in his eagerness to associate with other men, rather than claiming the final prize. The lawyer's character is very dynamic. He starts as a young, impatient person, ready to spend 15 best years of his life for 2 million. His imprisonment changes his life positively: he reads books, ponders over scriptures, learns languages and plays the piano. His character is reflected when he renounces the 2 million and settles with just having proved his point.
The banker likes to be in a position of authority and likes to wield power over others, especially those who happen to disagree with him. The character changes drastically from the beginning of the story when he seems to be very free handed as he easily bets to pay two million and later, his lack of wealth drives him to dishonesty and plan for murder. This also signifies the weak character of the banker. He is very attached to the materialistic luxuries of life and values human life less than his luxuries as he plans on killing the lawyer. He plans on killing the lawyer for money and nothing but money changes his mind.