Johnny Mnemonic is the main protagonist in the 1995 science fiction-thriller film Johnny Mnemonic. He is protrayed by Keanu Reeves, who also portrayed "Ted" Theodore Logan in the 1989 comedy film Bill & Ted's Excellent Adventure and the hit 1991 sequel Bill & Ted's Bogus Journey, Johnny Utah in the 1991 action film Point Break, Jonathan Harker in the 1992 horror film Bram Stoker's Dracula, Officer Jack Traven in the 1994 action film Speed, Neo in the 1999 action-thriller film The Matrix, the 2003 sequels The Matrix Reloaded and The Matrix Revolutions, and John Wick in the 2014 neo-noir action-thriller film of the same name, and it's two sequels: the 2017 John Wick: Chapter 2, and the 2019 John Wick: Chapter 3: Parabellum.
In 2021, Johnny is a "mnemonic courier" with a data storage device implanted in his brain, allowing him to discreetly carry information too sensitive to transfer across the Net, the virtual-reality equivalent of the Internet. While lucrative, the implant has cost Johnny his childhood memories, and he seeks to have the implant removed to regain his memories back; his handler, Ralfi assigns him one more job that would cover the costs of the operation (which are extremely expensive), sending Johnny to Beijing to deliver the latest information.
On the way to the job, in the elevator he uses a Pemex Memory Doubler to upgrade his memory capacity from 80 gigabytes to 160 gigabytes. At the designated place, he finds a group of frantic scientists watching anime who have the data he is to carry, but at 320 GB it far exceeds Johnny's storage capacity, even with the use of compression folders to decrease the size of the information, and if he tries to upload the data in, the remaining amount of data will be uploaded directly in his brain, causing severe psychological damage and potentially, death. Johnny accepts anyway, in need of the money. After uploading their data, the group is massacred by Yakuza, but Johnny manages to escape with a portion of the encryption password.
After contacting Ralfi, Johnny returns to Newark and soon finds that two groups are after the data he carries. One is the international pharmacological company, Pharmakom, led by its United States executive, Takahashi, who believes the data to be critical to the company's interests. The other is the Yakuza guided by Shinji, who wishes to deny this information to Takahashi and claim it for themselves. Johnny soon learns that Ralfi is in the Yakuza's employ, and ready to kill Johnny to extract the data storage hardware. Jane, a cybernetically-enhanced bodyguard, helps Johnny to escape, and aided by the Lo-Teks, an anti-establishment group led by J-Bone, they elude their pursuers.
Jane takes Johnny to meet her friend and street doctor Spider who had installed Jane's implants. In discussions, Spider reveals he and his allies at a local clinic were to be the recipients of Johnny's data, supposedly Pharmakom's unpublished cure for "nerve attenuation syndrome", a plague ravaging mankind, due to the over-reliance on technology, and causing political strife. Though Spider could remove Johnny's implant, this may cause both the loss of this invaluable data as well as Johnny's life; instead, Spider directs Johnny to Jones, who resides at Heaven, the Lo-Tek base built on the underside of a bridge. The clinic is soon invaded by the assassin Karl, the Street Preacher hired by Takahashi to retrieve Johnny's head before Shinji can; Spider is killed while Johnny and Jane escape.
At Heaven, they find that Jones is a dolphin, once used by the Navy for his decryption capabilities. Jones attempts to discover the remainder of the password to the data, but Heaven is soon attacked by the Yakuza, Takahashi's forces, and the Street Preacher. Johnny, Jane, and the Lo-Teks fight off all three groups and emerge victorious, killing Takahashi, Shinji, the Street Preacher, and their agents. Takahashi, in a dying gesture, provides Johnny with a portion of the remaining password. While this helps, Johnny is told by J-Bone that he must "hack his own brain" to find the final portion, unlocking the data so that the Lo-Teks can download it and transmit it across the globe.
Johnny and Jones again start the procedure but find themselves helped by a mysterious artificial intelligence that operates from Pharmakom's mainframe, providing the last portion of the password to unlock the data. The data for the NAS cure is safely recovered and Johnny discovers he can now recall his memories of his youth, including his mother and family. As Johnny recovers from the process, he, Jane, and the Lo-Teks observe the Pharmakom building on fire, a sign that the cure's transmission was successful.