Brian Johnson is an unseen important character in Grand Theft Auto: San Andreas, subject to rumors and mysteries.
Brian Johnson was the youngest sibling in the Johnson family. He was the son of Beverly Johnson and sibling to Sweet, Kendl and Carl Johnson. During his lifetime, he lived in the Johnson family house in Grove Street and was a core member of the Grove Street Families. Brian Johnson is supposed to look like Carl Johnson since Emmet refers to Carl as Lil Brian, an implication that Carl resembles his brother. Even though Brian is never seen during the game, flashbacks from Carl Johnson's memory reveal that both the brothers created a lot of chaos and mess and had an overall better relationship. However, sometime prior to the events of 1992, Brian Johnson died and the fault was put on Carl Johnson for unknown reasons. It is never revealed as it how Brian died or who killed him, but it is implied throughout the game that Carl Johnson was negligent and could've stopped Brian's death. A fact that haunts CJ throughout his lifetime. Carl Johnson, out of guilt and hurt left Los Santos to Liberty City and didn't attend Brian's funeral until he returned in the year, 1992 when another one from his family, Beverly Johnson was shot dead by the Ballas. Carl Johnson arrived at the cemetery moments before the funeral and was confronted by an agitated Sweet, who lambasted Carl for running away from the death of loved ones. During the final mission, End of the Line, Carl goes to avenge his mother's death and mentions that he's going to take on Big Smoke in tribute to his deceased brother, Brian Johnson. He also mentions that it was his fault Brian died. These series of scattered conversations, hints and lines point towards a perplexing mystery known as Brian Johnson's Death.
CJ or Brian: Quit it! Moms will hear!
Kendl: Mom! They're up to something!
–A flashback from the past CJ hears in his head, during the mission In the beginning. It reveals that Kendl is complaining to Beverly Johnson that Brian and Carl are messing around the house. An example of the brotherly relation between Carl and Brian Johnson
Brian's Death Mystery
Upon the analysis of the situation about the events prior to 1992. It is suggested that Brian Johnson died because of the traditional rivalry between Grove Street and Ballas. Prior to 1992, the Ballas were the only gang loggerheads with Grove Street and Brian could be the victim of the start of the long-lasting gang war between the two gangs. It could also be possible that the hints suggesting CJ was at fault, is because Carl Johnson didn't defend his brother from being shot dead by the Ballas. This theory is more likely to be true and is generally an accepted version of Brian's death, although it is not confirmed by Rockstar.
Another theory relating to his death, suggest that Brian's death was a plot by Big Smoke, as part of Big Smoke's Alliance and his plan to take over Los Santos in cooperation with the Ballas and C.R.A.S.H. This theory has a major drawback which concludes that it's not true. Big Smoke's Alliance started in the year 1992, prior to the years when Big Smoke was still loyal to the gang and no evidence is present to support the idea of any foreign hand in Brian's death. Thus, leaving this theory as false.
Brian's Photo Mystery
When CJ gets a flashback from the past, it's because of the reason he holds an old photo featuring Kendl Johnson and an unknown sibling. It is largely disputed and debated that the person next to Kendl is either Carl, Brian, or even Sweet. Many CLEO modifications and flashback videos around the web include Brian Johnson and his model as based on this particular person. However, it is not confirmed that the person in the photo is either Brian or his brothers. More than likely, this is Sweet as he wears similar clothing in old prototype screenshots of the game and even wears them in the game's concept art. In addition, he is next to Kendl's prototype model.