B Dup used to be a loyal member to the Grove Street Families but began to move away from the gang and into dealing drugs. Dup begins to sell drugs in Los Santos, including to Barry "Bear" Thorne, whom he exploits into being his personal slave. B Dup has Bear clean his home in Ganton. B Dup is also later heard on West Coast Talk Radio, saying "the problem in the hood is that there isn't enough drugs in the hood".
Events of GTA San Andreas
Carl Johnson and Ryder attempt to recruit B Dup during the mission Cleaning the Hood to kill some Ballas drug dealers. B Dup declines their offer as the Ballas are responsible for bringing the drugs into the city which he does not want to fight against, and is more concerned with making profit by selling them.
Much later in the game, during the mission Beat Down on B Dup, Carl and Sweet visit B Dup in his new home in Glen Park, Kilo Tray Ballas territory. After Carl and Sweet retake Glen Park, they enter B Dup's house to face him. Big Bear cannot take anymore abuse from B Dup so he punches B Dup and leaves with Carl and Sweet. B Dup isn't seen again after that encounter, though it is likely that he is still alive.
B Dup works for Big Smoke as he refers to him as "the boss" during the mission "Beat Down on B Dup". It is likely that Big Smoke supplies him with drugs.