Sean Bateman

Sean is a twenty-one-year-old student from a wealthy family. He is very promiscuous and a heavy substance abuser, as well as a drug dealer in the employ of Rupert Guest. He becomes romantically involved with Lauren, a relationship he considers to be true love. It is also implied that Sean is bisexual, as he apparently becomes involved in a sexual relationship with Paul Denton. However, whether these encounters are real or simply a product of Paul's imagination is left ambiguous; Paul narrates sexual incidents between himself and Sean, while such incidents are absent from Sean's own narration.

Sean is very bitter, cynical, and rather dim-witted, and is prone to self-loathing as well. He is also heavily implied to be somewhat of a sociopath, showing incredibly impulsive behavior (sleeping with Lauren's friend Judy, and at one point, breaking a box of singles he owns for no reason at all) and having no consideration for other people. He attempts suicide at multiple points in the book, first by hanging, then by slashing his wrist with a dull razor, and then by overdose after a falling out with Lauren. A major subplot in the novel is Sean's debt to Rupert, a violent townie drug dealer who often threatens to kill him. The character is the brother of the notorious Patrick Bateman and has also appeared in Ellis's other novels, American Psycho, The Informers and Glamorama.

Lauren Hynde

Lauren is a painter and poet who has sexual relations with several boys on campus, all the while pining for Victor, her boyfriend who left Camden and headed to Europe. She is often depressed and very emotional. She is in her senior year at Camden. At the beginning of the novel, it is revealed that Lauren lost her virginity at a party during her freshman year at Camden, where she got so intoxicated that she passed out in bed with another student only to awaken and find herself being raped by a pair of townies. She becomes romantically involved with Sean Bateman halfway through the book, even though she holds Sean in contempt and considers the relationship nothing but a way to pass the time before Victor comes back from Europe. She was also in a relationship with Paul before the events of the book take place. In Glamorama, the character is revealed to have died shortly after the end of this novel. Her place is then taken by a body double who becomes reacquainted with Victor after having become a successful model and actress.

Paul Denton

Paul is a young bisexual man who used to date Lauren. He is extremely attracted to Sean and claims that in bed Sean is "crazed, an untamed animal, it was almost scary" yet these thoroughly described accounts are entirely absent from Sean's entries. For example, the night Paul writes an account of his and Sean's first sexual encounter after the two talk in Paul's bedroom, Sean writes in his own account that he simply went home after talking to Paul, the two entries therefore lying in contradiction to one another. However, the true details of this relationship remain ambiguous and open to the reader's interpretation. Paul also had relationships with two other important characters, Mitchell and Richard (Dick). Paul is highly intelligent and passionate, but is not above obscuring these facts in the course of seduction. Several characters in the book remark upon his physical attractiveness, brought out by Roman features and soft blond hair. Paul's relationship with his mother, Eve, is complex; she yearns to reach out to him but is led towards iciness by Paul's flippancy, which in turn feeds their animosity.

Supporting characters

• Victor Johnson – Lauren's boyfriend. Victor took the term off to backpack through Europe. During his time in Europe, he sleeps with many people and abuses many drugs. His entries consist of long diatribes listing his adventures, including a search for a girl named Jaime, who he claims to love. Lauren yearns for him, anxiously awaiting his return, and when he does come back to New Hampshire, he is not interested in seeing her at all. He is the main character in Ellis' later novel, Glamorama.
• Clay – The protagonist of Less than Zero, aka "the guy from L.A.", who narrates one chapter of the novel. His trademark lines begin "People are afraid to ...". Still unhappy while at Camden, Clay longs to return home to L.A.; he wishes the reverse in Less than Zero.
• Rupert Guest – A violent drug dealer and Sean's supplier. A major subplot in the book is Sean's debt to him.
• Richard "Dick" Jared – An old friend of Paul Denton's who attends Sarah Lawrence College. They are friends with benefits.
• Patrick Bateman – Sean's older brother, an investment banker who is much more focused and successful than Sean. The brothers loathe each other for their very different outlooks on and approaches to life. He narrates a chapter of the novel and returns as the main character of Ellis's follow-up novel, American Psycho, in which it is revealed that he is a serial killer or believes to be one.
• Sean's admirer – An unnamed student (although her name is probably Mary) who sends Sean anonymous love letters. Her entries in the book are all italicized letters to Sean. She hopes to reveal herself to Sean at the Dressed To Get Screwed Party midway through the book, but when she sees him leave with Lauren, she is heartbroken and commits suicide in a bathtub by slashing her wrists.
• Bertrand – Sean's French roommate, whom he despises. Sean continuously refers to him as "The Frog." He pines for Lauren and narrates one section of the book entirely in French. He also appears in Glamorama with an intense hatred for Victor from the anguish he had caused Lauren.
• Stuart – A student who moves into the room across from Paul Denton. He previously had a crush on Paul when they shared a drama class, from which Stuart subsequently withdrew after he botched a scene with Paul. He later hopes to run into Paul after he moves across the hall, and hopes (unsuccessfully) to see him at the Dressed to Get Screwed Party. He also has a friend named Dennis.
• Mitchell Allen – A previous fling of Paul's who has reverted into the closet. He later reappears in Ellis' Lunar Park.
• Roxanne - A friend of Lauren's who, like Sean, gets drugs from Rupert. Roxanne dates Rupert during the novel and Sean states that he was also seeing her at one point.
• Judy - A friend of Lauren's who sleeps with Sean after a party, which ruins Sean and Lauren's relationship.