Billy was employed as a trainee Metrocop for the Combine and worked alongside his best friend Dan Mason. He was referenced as "Officer Blobby" due to being overweight and was often mocked and jibed. Despite this though he proved himself during a zombie invasion in City 17, which was later dealt with.
After the Combine's downfall Billy lost his job as a cop so took up office work instead and was stationed at the same place as his father Nathan Johnson.
Getting bored of office work, Billy decided to set up his own bar and borrowed a large sum of money from a loan shark named Campbell Stanton. Stanton agreed to help Billy, on the condition he gives him a cut of the take. But when Stanton became threatening and beat Billy on an occasion, Billy reported Stanton to the police and he was arrested and remanded in custody. Billy hoped that with an assault charge Stanton would be locked away and he would be debt free.
Billy got involved with the Simmons crime family and took part in a bank heist.
But Billy's world would come crashing down when Stanton was released from prison after only serving five months. Stanton began threatening Billy for the rest of his payment. Billy decided not to turn to his father, and decided to burn down his now failing bar to pay off his debts. But this had major repercussions when Billy got trapped when the fire blocked the exit, and he was unable to fit through the window due to being overweight. Fortunately though Billy was saved although he fell into a coma. Stanton was arrested on suspicion of starting the fire when surveillance footage was found showing him harassing Billy. A vengeful Nathan used his contacts in the Simmons family to get Stanton beaten and mutilated in prison. Billy got off with arson, and Stanton faced ten years in prison for arson.
After the Simmons crime family fell, it was discovered Dan was a detective working undercover. He pardoned Billy along with Nathan (who was presumed dead after being shot) and also their friends Simon Simms and disgraced boss Don Simmons. Billy began to work with Dan as an informant and to try and uncover corruption in City 17 and to deal with remaining criminals once afflicted with Simmons. This put them into a small conflict with Frank Blackstone, who was attempting to takeover the City 17 Underworld.
Following his father's death years later, Billy changed his outlook on life and putting behind any last moralistic views, decided to become a criminal.
- Billy uses the Heavy model from Team Fortress 2. Versions of the character use a black suit and tie and sometimes a hat.
- Billy was first introduced in the second Halloween Special titled Night of the Living G-Men, but was credited as Officer Blobby and nothing was said about his relation to Nathan Johnson. When the character returned two-years later, he was credited as Billy Johnson and his connection to Nathan was established.