The town eccentric, Pudd'nhead Wilson first came to Dawson's Landing intending to set up a law practice. His sense of humor proves too much for the townspeople, though, and his law practice goes nowhere. He fills his time with odd surveying and accounting jobs, and dabbles in a number of quasi-scientific hobbies, most notably fingerprinting and palmistry. Judge Driscoll is his closest friend. Pudd'nhead has also written a calendar full of clever sayings and dark proverbs, which provides the epigraphs for each chapter of the text. Pudd'nhead is an outsider, and thinks a little differently from the rest of the townspeople.
Roxana, called Roxy, begins as a slave owned by Percy Driscoll. Only one-sixteenth black, she looks white, and is described as an extremely beautiful woman. She gives birth to a son, Chambers, who will later be known as "Tom" when she switches him with another infant. Roxy is tough, intelligent, and resourceful, and, although she is freed when Percy Driscoll dies, she is the character most threatened by slavery.
Roxy's son. At a young age he is switched by his mother with Thomas a Becket Driscoll, a white child who shares his birthday and looks just like him. From then on he is known as "Tom." Raised as a white heir to a substantial estate, "Tom" is spoiled, vicious, and dissolute. His penchant for gambling leads him into debt, and his "uncle," Judge Driscoll, frequently disinherits him, only to rewrite his will again.
The son of Percy Driscoll, Tom is switched with Roxy's baby Chambers when he is only a few months old, and is called "Chambers" from then on. "Chambers" is raised as a slave and is purchased by Judge Driscoll when Percy dies to prevent "Tom" from selling him "down the river." "Chambers" is a decent young man who is often forced to fight bullies for "Tom." He speaks in a black dialect.
A member of a prominent Virginia family, the judge is a leading citizen of Dawson's Landing. He and his wife are childless, but adopt "Tom" when the judge's brother, Percy Driscoll, dies. The judge is powerful enough to indulge his eccentricities, and he forms a philosophical society with Pudd'nhead Wilson after he retires from the bench. The judge is wealthy and generally kind-hearted, and supports "Tom," even paying his gambling debts.
Luigi and Angelo Capello, a set of near-identical twins, appear in Dawson's Landing in reply to an ad placed by Aunt Patsy, who is looking for a boarder. They say they are looking to relax after years of traveling the world. They claim to be the children of an Italian nobleman who was forced to flee Italy after a revolution and died soon afterward. According to their story, they were enslaved by a traveling circus and put on display (in the first version of Twain's story they were Siamese twins). After several years they escaped and went into business for themselves, putting themselves on display. The twins are good-looking and smooth-talking, and the townspeople fall over themselves trying to be associated with them. Luigi has a dark secret in his past, though: he once killed a man who tried to rob them and was about to kill Angelo. Luigi's temper gets him into trouble in Dawson's Landing, too: he assaults "Tom" after "Tom" insults him. This leads to a duel in which the twins, with their old-world traditions, are only too happy to take part. While they seem suspicious, the twins are never unmasked as conmen; instead, they leave Dawson's Landing vindicated and triumphant.
Judge Driscoll's brother and Tom's father. A speculator, he dies when Tom and "Tom" are fifteen, with his estate heavily encumbered by debt. Shortly before he dies, he frees Roxy, who was his slave.
A lawyer, a close friend of Judge Driscoll, and another descendant of what Twain calls the "FFV's"- -the First Families of Virginia. Pembroke Howard supports the judge in his ideas about Virginian honor. He is the one who prosecutes the twins for the judge's murder.
Judge Driscoll's widowed sister and "Tom"'s surrogate mother. She helps to keep "Tom" in the judge's good graces.
Yet another Virginian and friend of Judge Driscoll's. He dies the same year as Percy Driscoll. Roxy reveals that he is the father of her son (Chambers). Her revelation explains the rather awkward introduction and dismissal of Colonel Essex in the first chapter.
The widow, known to the town as Aunt Patsy, takes the twins in as boarders. She and her daughter Rowena fan the flames of the twins' celebrity for their own benefit. Everyone is at her house when the string of robberies takes place.
Aunt Patsy's daughter and the town belle. She epitomizes the townspeople's intense response to the twins. The narrator hints that she may have been involved with "Tom" romantically.