This page contains information regarding Star Trek: Picard, and thus may contain spoilers.
B-4 was a prototype android constructed by Doctor Noonian Soong on Omicron Theta in the 2330s. He was one of three failed prototypes and the only one to survive a significant amount of time after his activation before the construction of Lore was successful. (TNG: "Inheritance") Although B-4 was outwardly identical to both Data and Lore, the two final androids built, B-4 was not equipped with a positronic brain as sophisticated as those of his brothers. As a result, he had difficulty understanding simple concepts and processing information.
The existence of B-4 was not known to Starfleet until 2379 when the disassembled pieces of the android were found by the crew of the USS Enterprise-E on Kolarus III, although he could not remember anything about his existence prior to Kolarus III or how he ended up there. The crew of the Enterprise subsequently reassembled him. Although he recognized B-4's limitations, Data wished to give his brother the opportunity to expand his capabilities, much in the same way that he himself had in years past. To that end, Data willingly copied all of his memories to B-4, hoping that the added experiences would help B-4 to expand beyond his original programming. However, he was unable to immediately assimilate Data's memories and could not remember things Data could, such as the layout of the Enterprise, Dr. Soong or Captain Jean-Luc Picard.
In actuality, B-4's pieces had been planted on Kolarus III by Shinzon as part of an elaborate scheme to lure Captain Picard near Romulan space in order to capture him. B-4 was also used as an unwitting spy; he was equipped with a second memory port that contained subversive programming that compelled him to download vital information about the positions of all Federation starships and their coded communications frequencies. However, Data and Lieutenant Commander Geordi La Forge discovered B-4's unauthorized access and indefinitely deactivated him. Data posed as B-4 and provided Shinzon with inaccurate locations for all Starfleet vessels as well as assisting Captain Picard in escaping from Shinzon's ship, the Scimitar.
A short time later, Data perished while destroying the Scimitar, having voluntarily sacrificed himself to save Captain Picard. B-4 was reactivated so that Picard could tell him of his brother's death, but Picard sadly departed the meeting when his attempts to explain what Data meant to them only confused B-4. With his future uncertain, Picard had noted some of Data's downloaded memories beginning to surface as B-4 begun to sing the song "Blue Skies", which Data had performed at Will Riker and Deanna Troi's wedding. (Star Trek Nemesis)
B-4, disassembled, was in storage at the Division of Advanced Synthetic Research at the Daystrom Institute when Picard visited after his retirement. According to Dr. Agnes Jurati, B-4 was "not much like Data at all," and most of Data's positronic network was lost after the transfer. (PIC: "Remembrance")
Background information Edit
B-4 was played by actor Brent Spiner.
According to the original Star Trek Nemesis script, the android B-4 ("before") was named "B-9" ("benign"). After detecting the positronic signature from Kolarus III, La Forge asks Data how many androids Dr. Soong built with Data replying he was only aware of himself and Lore. Also according to the script, the android was taken from its homeworld by the Pakleds and traded to the Bolians. He ultimately encountered some Cardassians, who tossed him into a garbage chute and out into space, where he was found by Talosians. It was also revealed that Shinzon had learned of the prototype android through a Cardassian historian. Shinzon had planned to force B-4 into slave labor after carrying out his plans against Picard and the Federation. None of this, however, made it to the final version of the film. The novelization names him as "Be-Fore." A deleted scene from the film shows Data trying to teach B-4 to eat with a spoon in the Enterprise crew lounge, but he cannot grasp the skill, much to Data's disappointment.
B-4 is deactivated and sent off to the Daystrom Institute for Analysis in the novel Resistance, Picard and La Forge having come to accept that the moments where B-4 acts like Data are merely random sparks rather than any sign that B-4 has significantly progressed as a sentient being.
In the novel Cold Equations: The Persistence of Memory, Doctor Bruce Maddox is contemplating deleting Data's memory engrams from B-4, who is kept in storage along with the remains of Soong's other prototype, Lore, and Lal, Data's daughter, when they are stolen by the Breen. Doctor Soong – who survived his death by transferring his mind into an android body far more Human in appearance than Data's – manages to recover his "children", and transfers Data's memories from B-4 into his own body, unable to complete the new body he had been attempting to construct for his "son".
The comic book series Star Trek: Countdown (a tie-in to the 2009 Star Trek film) and the timeline established for the Star Trek Online game depict Data as alive in 2387. Sometime prior, Geordi La Forge installed Data's emotion chip into B-4's neural net. This caused the uploads to B-4 by Data to fully activate, allowing Data's full memory and personality to assert itself, essentially resurrecting him. Starfleet decided to reinstate the android to service and, by the time of Countdown, Data had become captain of the USS Enterprise-E. The reactivated Data and Spock later converse on their respective "resurrections."
The "Guardians" story in Strange New Worlds VII dealt with the Horta culture being transplanted to the planet where the Guardian of Forever resided. The Crystalline Entity visited the world almost a thousand years after the events of Nemesis and described an encounter where it was forced to destroy B-4.