Brian is the youngest known child of Beverly Johnson and the sibling of Carl, Sweet and Kendl. He apparently bore a strong resemblance to Carl, as Emmet initially mistook Carl for Brian when they first met.
Brian was associated with the Grove Street Families due to being the younger brother of the gang's leader, Sweet. He had wanted to be in the gang, but had either no time or a short time in the gang. Brian lived in the Johnson House, Ganton, Los Santos until his death in 1987.
Brian was killed in 1987. Plots about that event are unknown, but it possibly that a rival gang played a part in Brian's death. Carl himself was present during Brian's death.
After Brian's death, Sweet blamed Carl for his death, which led to Carl leaving Los Santos for Liberty City for the next five years. Carl did not attend Brian's funeral, confirmed when Sweet says: "That's another funeral you ran away from, fool. Just like Brian's".
Events of GTA San Andreas
Brian's death plays a big role in Carl and Sweet's relationship.
In 1992, Carl returns to Los Santos after his mother, Beverly, was killed by the Ballas. He missed the funeral, making Sweet angry at Carl for missing another one.