Carl Francis Hashish Gallagher was born to Monia & Frank Gallagther, in January 2002. He was the second-youngest Gallagher child. Carl was often in trouble at school for attacking other students. In his early years, he displayed several psychopathic tendencies such as mutilating his toys and killing stray animals, although this behaviour seems to wane as he got older.

Frank convinced him he had cancel and shaved his head so he could scam the children in need foundation. He was then told that his cancer had been cured.

His love for selling drugs started at age ten, when his grandmother Peggy convinced him to get prescription drugs to make meth. Carl begins selling drugs for a local gang which Fiona discourages and Frank encourages. He later used his nephew Chuckie in his illicit schemes, but both were caught and sentenced to juvenile detention. Although Fiona begged him to betray his gang associates to receive a lesser sentence, Carl refused as he wanted the "street cred" juvie would give him. He was made a full member of the gang for his loyalty.

When he is released from prison, he immersed himself into gang culture. He started selling firearms with his friend Nick. However, after someone stole his bike, Nick murdered the kid and got arrested. This traumatized Carl and he decides to give up his criminal ways and was eventually allowed to leave the gang.

Carl enrolled in military school, which helped him be more responsible and mature. He graduated but because he stood up to his unit for attacking a transgendered student, he was not allowed to serve in the army. Still wanting to do some good in the world, he becomes a police officer, but struggles with all of the issues he finds.

Carl and his former partner, Arthur, consider buying the Alibi Bar together and turning it into a cop bar.