The main characters in On the Road are Dean Moriarty, an aspiring writer and part-time railroad worker, and Sal Paradise, the story's first-person narrator and a young author. Dean serves as Sal's alter ego, embodying the experiences Sal wishes to document in his writing—fully immersing himself in life's moments. Throughout the book, Sal and Dean's identities are intricately intertwined.

Dean is a radical innocent, naturally rebelling against conventional moral standards. Raised without a mother by a vagabond father, he represents the dynamic spirit and vitality of the American West, inspiring Sal and his intellectual friends to take action. Dean, once a convict and high school dropout, reads Proust and dreams of becoming a writer, but his talent lies in movement, not writing. Disillusioned with modern values, he lives a hectic life filled with travel, multiple marriages, and substance use. From his enigmatic, darker brother, Sal learns the allure of the open road and the importance of spontaneity.

Kerouac was open about the fact that Dean's character was directly inspired by Neal Cassady, and that Sal was a self-portrait. Writing "personally, factually," Kerouac based his characters on his real-life friends, altering only their names. Carlo Marx represents Allen Ginsberg, while the reserved Bull Lee is modeled after William S. Burroughs. As with much of Kerouac's work, even the minor characters are drawn from real life.