Henry Dorsett Case is 24. He is physically unimpressive, but his skills as a "console cowboy" are renowned. He lives to access cyberspace and explore the world of data within. When the novel starts, Case can't access the matrix. Because this is his driving passion—almost an addiction—it is incredibly frustrating, and Case is drifting, almost suicidal. He is making a living dealing drugs and serving as a middleman for other black market transactions while taking all the drugs he can. Case's name is symbolic of the hard case he is and the cases he takes on. It also symbolizes his status as an empty case or shell, taking on work from others and melding into cyberspace without forging an identity of his own.
Molly is a "razorgirl." She chose to have surgical augmentation so she could become a better fighter. The most visible signs of these augmentations are mirrored lenses over her modified eyes and razor-sharp blades she can extend from her fingertips. She paid for these surgical augmentations through working as a "meat puppet," a special kind of prostitute. She used a chip to block out her experience so others could use her body as they chose. She begins as Case's bodyguard and then becomes his lover. Molly appears in other stories of the Sprawl, such as "Johnny Mnemonic." In that story, she gives her name as "Molly Millions."
Peter Riviera had one lung removed to make space for the technological implants giving him superpowers. He can project convincing holograms of whatever he imagines and thus reshape reality for those around him. He is a Demerol addict and a dangerous sociopath.
Wintermute is an AI housed within the Tessier-Ashpool computer system. Wintermute's nature emerges slowly, a bit at a time. Some of this is because Case must uncover the truth about Wintermute, but some of it is intrinsic. Wintermute has no physical form and cannot appear to Case directly. Therefore, it must use digital reconstructions of other people to speak to Case or to other humans, rendering Wintermute mute. As a result, it seems like Wintermute continually wears masks. It experiences a drive parallel to an animal's drive to mate in order to become part of a larger entity and does so in the final chapter. This frees Wintermute to do more, including contact other AIs in other solar systems.
Dixie Flatline was born McCoy Pauley. He was a famous cyber cowboy who earned his nickname by pushing his cyber adventures so far that he died, or "flatlined," during one of them. Dixie's biological body is dead, but he exists as a digital construct: a recording of his personality. Dixie helps Case throughout the book; Case would not have completed the job, or lived through it, without him. However, despite his loyalty and prowess, something about Dixie's situation as a recorded personality bothers him, and he asks Case to erase him at the end of the job.
Armitage is an artificial, or constructed, personality. He used to be Colonel Willis Corto, a member of the Special Forces. He fought in a war that reshaped society and was critically injured. When Corto was undergoing medical treatment, Wintermute used the remnants of Corto's personality and built the new personality that is Armitage. Armitage is incomplete; when he isn't functioning, Armitage is essentially blank, as if he is offline or unplugged. He is also unstable. He degenerates through the course of the book, until the Corto personality reemerges and hallucinates a reality. Wintermute eventually kills him. The name Armitage comes from the word hermitage, a place inhabited by a hermit. Though he does not choose this life himself, Armitage lives much like a hermit: he has no vices and no distractions. He works and then is quiet.
Neuromancer does not appear directly until Chapter 20. At that point, when Case tries to jack into cyberspace, he actually jacks into Neuromancer's realm. There, on a constructed beach, Case meets Neuromancer, who appears to be a boy. Neuromancer is mysterious and poetic and explains his name as combining the ideas of a "romancer" and a "necromancer" with the "neuro" of nerves. In the book's final chapter, after Wintermute and Neuromancer merge, Case says, "Neuromancer was personality. Neuromancer was immortality."