The B-4 matrix, like the Data matrix, was the personality, consciousness and memories of the android B-4. After Data had been restored by creating the Data Matrix within B-4's body, B-4 deleted himself to allow Data to survive. However, the science team from the Soong Foundation had saved a backup copy of B-4, and began work on creating a B-4 matrix with the hopes of someday restoring him in a new body. (STO novel: The Needs of the Many)