Algernon is a mouse that earlier underwent the same operation as Charlie. Algernon becomes an expert at running highly complex mazes. Charlie competes with Algernon in maze races. As the experiment progresses, Algernon's demeanor becomes unpredictable and aggressive. This signals a problem with the experiment. Eventually, Algernon's abilities radically regress, and he dies. Charlie comes to love the mouse and buries Algernon in his backyard, often placing flowers on the mouse's grave.
Mr. Donner is Charlie's boss and the owner of Donner's Bakery. He hires Charlie at the request of Charlie's Uncle Herman, promising that as long as he lives Charlie will have a job. Donner believes in Charlie, but eventually dismisses him at the request of his other employees.
Gimpy, Joe Carp and Frank Reilly
Gimpy, Joe Carp, and Frank Reilly are Charlie's co-workers at the bakery. Initially, these men delight in playing pranks on and making fun of Charlie. They resent the more intelligent Charlie when he returns to his job after the operation and eventually get Charlie fired. However, at the end of the novel, when Charlie's intellectual level has dramatically receded and he returns to the bakery, they defend and vow to protect him.
Charlie Gordon is the novel's main character. He is a 32-year-old janitor employed at a bakery. At the beginning of the novel, Charlie has a very low IQ but attends remedial night classes for reading and writing at Beekman School for Retarded Adults, part of Beekman University in New York. He attends the classes because he has always had a desire to learn. Though he is of limited intelligence, Charlie is a hard-working, honest man. He lives on his own and feels that he has true friends at the bakery. Unfortunately, he is gullible and is frequently the butt of jokes by his co-workers.
Charlie agrees to participate in an intelligence-enhancing experiment and undergoes an operation. The procedure dramatically increases Charlie's intelligence, tripling his IQ. As a result, he experiences a tremendous change in his intellectual ability. At the same time his emotional and personal life are also radically transformed, causing him much mental pain and anguish. Unfortunately, the procedure's effect is not permanent, and Charlie eventually regresses to his original state of mind.
Matt Gordon is Charlie's father. Matt is more realistic than Rose about Charlie's abilities and is more comfortable with Charlie as he is. In the beginning of the novel Matt is a salesman of barber shop supplies. He eventually leaves Rose and Norma and opens his own barber shop. He does not recognize Charlie when Charlie returns to visit him.
Norma Gordon is Charlie's younger sister. Other children tease her about Charlie; as a result, she develops a strong dislike of him. When Charlie visits his mother and sister late in the experiment, Norma is shocked, stating that Rose informed her that Charlie had died years ago at the Warren Home. Norma tells Charlie that she would welcome his return to the family.
Rose Gordon is Charlie's mother. For the first few years of Charlie's life, she desperately wants to see her son as normal and steadfastly defends him. She takes Charlie to numerous doctors in an attempt to improve his mental ability. However, when Norma, Charlie's sister, is born, Rose's position reverses; she begins to distrust and to even dislike her son. She eventually forces her husband to remove Charlie from their home and remand him to the care of the Warren Home.
Charlie is taken to Dr. Guarino at his mother's insistence. Guarino claims he can enhance Charlie's intelligence with a procedure that involves strapping Charlie to a table and subjecting him to a visual/auditory stimulus device. Charlie later comes to view Guarino as a charlatan.
Charlie's Uncle Herman, an overweight house painter, is responsible for getting Charlie discharged from the Warren Home and for getting him the job at Donner's Bakery.
Hilda is Charlie's first nurse after his operation. She suggests that perhaps the operation should not have been performed because it was tampering with God's will.
Miss Alice Kinnian
Miss Alice Kinnian is Charlie's teacher at Beekman School for Retarded Adults, where Charlie attends remedial night classes in reading and writing. She develops a close personal relationship with Charlie and eventually falls in love with him. She enjoys their relationship in the initial stages of Charlie's intellectual rising, but feels alienated when his intelligence surpasses her own. Though they become estranged, she returns to take care of Charlie when his intelligence eventually declines.
Fay Lillman is Charlie's artistic neighbor at his second apartment in Times Square. She is a painter, and Charlie finds her attractive. They engage in a whirlwind romance predicated on nightly drinking and dancing in local clubs. As Charlie's time runs out, he tires of the routine and spends less and less time with her. Charlie attempts to reconnect with Fay when his intelligence begins to recede, but she is frightened of him.
Bertha Nemur is Professor Nemur's overbearing wife. She has played a large role in her husband's career and is responsible for procuring the funding for the experiment from the Welberg Foundation.
Professor Harold Nemur
Professor Harold Nemur is a psychology professor at Beekman University and is the senior scientist in the experiment. Nemur is somewhat insecure personally and professionally, and he enjoys taking credit for Charlie's enhanced intelligence. He usually treats Charlie more as a test subject than an individual human being.
Burt Selden is a graduate student majoring in psychology at Beekman University. He administers various tests to Charlie throughout the experiment. Selden seems to genuinely care about Charlie as an individual.
Dr. Jay Strauss
Dr. Jay Strauss is a psychiatrist and neurosurgeon at Beekman University. He is a colleague of Professor Nemur and is co-director of the experiment. He performs the operation on Charlie and also psychoanalyzes Charlie throughout the experiment.