Jim Smiley is the central figure in Simon Wheeler's tale. Residing in Angel's Camp, Calaveras County, around 1849 or 1850, Jim is infamous for his passion for betting on almost anything, no matter how absurd. He’s known to have bet on people recovering from illness and even on which of two birds would fly away first. Jim would make even the most unlikely bets just to have the opportunity. Despite this, he was considered lucky and often won. Jim owned several animals: an old horse, a bull-pup named Andrew Jackson, cats, chickens, and a frog named Dan'l Webster, the "celebrated frog" referenced in the story's title. Jim leveraged these animals' skills for many of his bets. However, he was outsmarted by the Stranger at the story's end, contrasting with Twain's experience of being deceived by the local, Simon Wheeler.

Twain explores these themes in multiple ways throughout his story. Simon Wheeler, for example, epitomizes the American westerner—a talkative old man who spins exaggerated and highly improbable yarns. He speaks in a monotonous tone, seemingly unaware of the storytelling techniques that captivate an audience. An uneducated man, Wheeler narrates his story in the popular format of the tall tale rather than one of the more esteemed classic genres taught in eastern schools. He also uses vernacular language, which includes colloquial expressions, slang, and incorrect grammar and syntax. Wheeler’s use of vernacular underscores the notion that the West is inhabited by unsophisticated individuals with little education or mastery of proper speech.

Simon Wheeler is an elderly resident of the western mining town known as Angel's Camp. Described by Twain as a fat, balding man with "an expression of winning gentleness and simplicity," Wheeler is found in a bar. He recalls the early days when much of the camp was being constructed and shares the actual tale of the notorious gambler Jim Smiley and his "celebrated jumping frog." Although Wheeler appears comfortable in his role as storyteller, he seems unaware that he is boring his listener, Mark Twain, and oblivious to the fantastical nature of his tale. Twain notes that, despite Wheeler's lengthy and monotonous delivery, he speaks sincerely and takes his stories seriously. Critics, however, suggest that Wheeler is more aware of his narrative skills than he lets on and is not as naive as he appears. Despite his seemingly unsophisticated demeanor, he quickly assesses the refined easterner and tricks him into listening to his elaborate story.

In stark contrast to Simon Wheeler, the narrator, Mark Twain, appears cultured and well-educated. This version of Mark Twain is also a storyteller, but in the sections that frame Wheeler's tale, he speaks in polished English. It is evident that he is knowledgeable about proper grammar and syntax. However, Twain also comes off as somewhat elitist. He is irritated by Wheeler's language and dismisses Wheeler's quaint stories as lacking in worth because he finds them fantastical. Indeed, when Wheeler is momentarily called away, Twain seizes the opportunity to slip away, unwilling to listen any further. Twain does not regard Wheeler as an effective storyteller because the old man does not adhere to the conventions Twain values. He fails to recognize, however, that Wheeler is cleverly playing into the stereotype of the uneducated westerner. For example, although Twain perceives Wheeler’s voice as monotonous, it convinces him that Wheeler speaks with sincere earnestness. Wheeler skillfully balances the absurdity of his tale with the gravity of his delivery to keep Twain engaged.

Mark Twain serves as both the author and narrator of the story, as well as one of its characters. He is portrayed as the target of a joke—the unwilling audience for the fantastic tales of a talkative old man named Simon Wheeler. Twain was supposedly asked by a friend to find out about an acquaintance of that friend. However, Twain believes this was merely a trick and becomes frustrated by his entire experience with Wheeler. He comes across as an impatient, condescending man unwilling to listen to Wheeler and sneaks away when he gets the chance. Speaking in perfect English, Twain can be seen as a symbol of the snobbery associated with the eastern United States during the nineteenth century.

Dan'l Webster is the "celebrated jumping frog of Calaveras County." Captured and trained by Jim Smiley, Dan'l was taught to jump high, far, and on command. When jumping, he performed somersaults and is described by the narrator as "whirling in the air like a doughnut." Despite his impressive jumping skills, he is characterized as modest and straightforward. He was often used in Jim's bets and fell victim to the stranger's trick. According to Jim, Dan'l Webster could outjump any frog in Calaveras County. He shared his name with the famous nineteenth-century American statesman and orator.

Jim Smiley frequently used his bull-pup, Andrew Jackson, for betting purposes. This dog, although not particularly impressive in appearance, often seemed to be outmatched in fights with other dogs. However, the narrator observes that Andrew Jackson remained unperturbed by these initial setbacks. When a wager was at stake, his demeanor would shift. As the bets increased, Andrew Jackson would latch onto his opponent's hind leg and hold on until the other dog's owner conceded defeat. In this manner, Jim's bull-pup would secure victories. Andrew Jackson eventually died after Jim set up a fight with a dog that had no hind legs. The narrator suggests that Andrew Jackson, being a proud dog, succumbed to embarrassment. Similar to his namesake, Andrew Jackson is depicted as resolute and strong-willed.

The Stranger is a swindler who challenges the prowess of Jim’s frog, Dan'l Webster, claiming that any other frog could outperform him in a jumping contest. While Jim searches for another frog, the Stranger secretly feeds Dan'l Webster quail shot, making him too heavy to jump. As a result, he cheats Jim out of his money. This scenario, where the Stranger deceives the local (Jim Smiley), contrasts with Simon Wheeler, the local, deceiving Twain, the visitor.

The Fifteen-Minute Nag is the name of Jim Smiley's horse. Despite being old and rather sickly, Jim frequently used her in his bets. The horse, afflicted with various ailments, didn't seem like a contender in races. Nonetheless, Jim would enter her in competitions. Though she started slowly, in the final stretch, the nag would always muster the energy to get excited and usually win the race.