The hero of Pudd'nhead Wilson, David Wilson gets his nickname from residents who don't understand a witty remark he makes when he first arrived in town. He is earnest and likable and has recently graduated from law school. Still, for more than two decades, residents are reluctant to give this "pudd'nhead" (short for puddinghead, or know-nothing) a chance to practice law. Wilson's hobbies, however—palmistry and the study of fingerprints—and a sound ability to appraise human character eventually come to his rescue. Using them, he solves his adopted town's greatest mystery and becomes mayor.
Although in appearance Roxy is "as white as anybody," she is 1/16th black. In the 1830s antebellum (pre–Civil War) South, this meant she was black and, as a slave, salable, as were her children. Afraid her son might be sold, she switches him with her master's son, both children having been born on the same day. Roxy is eventually freed. However, her hopes that her son might be her salvation in her later years are dashed when she realizes she has indulged him too much and cannot depend on him.
Roxy likes the sound of the term Valet de Chambre (French for manservant) and gives the name to her newborn son. Like his mother, he is born a slave, but he has her light complexion. To save him from being sold, his mother switches him with the master's infant son, who was born on the same day. Roxy is able to raise the two boys together but dotes on her son, spoiling him. He grows up to be selfish and undependable and is even willing to sell his mother down the river.
Tom, named for the English martyr and saint Thomas à Becket (c. 1118–70), is the son born to landowner Percy Driscoll on the same day Roxy gives birth to her son. To Tom's misfortune, Roxy switches the two children to save her own son from slavery. Tom therefore grows up as Chambers, a slave. When he gets justice at the end of the novel, he is ignorant and unable to adjust to the white world. However, the African American world is closed to him.
Judge Driscoll's name combines the names of two cities in England. York is the name of a royal English house that yielded several kings of England. He is the brother of Percy Driscoll, and when Percy Driscoll dies, the judge takes in his nephew Tom, who is actually the slave Roxy's son. Judge Driscoll's wife dies shortly afterward. He and his widowed sister, Mrs. Pratt—who lives with him—indulge their nephew. The judge adheres to the unwritten code of the southern gentleman and is even willing to fight a duel on his ward's behalf.
Luigi is one-half of the famous Capello twins, who come to settle in Dawson's Landing. Luigi is more hot-tempered than his brother, Angelo, and in the past he killed a man to save his brother's life. Luigi is also increasingly intolerant of Tom's shenanigans and publicly kicks him, which draws a challenge to a duel from Judge Driscoll. The ensuing bad blood between Luigi and the judge provides a motive for authorities to charge Luigi with the judge's death.
Angelo, Luigi's brother, is the fair-haired twin. He arrives in Dawson's Landing with his more volatile brother, who once killed a man to protect him. Luigi kicks Tom Driscoll after Tom ridicules Angelo for being a teetotaler (a person who abstains from alcohol) at a rally in support of the strong rum party. Always in the background but always at his brother's side, Angelo is accused of being an accessory in the murder of Judge Driscoll.