Gus Fring served as one of the most dangerous antagonists featured in Breaking Bad, but his presence in Better Call Saul proved just how little viewers knew about the "chicken man." Giancarlo Esposito was cast to play the drug kingpin beginning in Breaking Bad season 2. He emerged as a key enemy of the protagonist, Walter White, before being taken out by his rival two seasons later. When creator Vince Gilligan created the prequel series, Better Call Saul, Esposito returned to the fictional universe, reprising his role as Gus, and the series managed to fill in many of the blanks regarding his past.
When viewers were first introduced to Gus, he was the co-founder of the successful fast-food chain, Los Pollos Hermanos. In reality, this fried chicken business was a front for his underground methamphetamine distribution. Based on his partnership with the DEA, Gus was able to hide in plain sight as he purchased an industrial laundromat to house a secret meth lab. Due to Walt's notoriety as "Heisenberg," he hired both him and his partner, Jesse Pinkman. Eventually the relationship soured, and Walt arranged for his former boss to be killed via an exploding wheelchair.
Though the Breaking Bad episode "Hermanos" offered a glimpse into Gus's distant past, his backstory really began unraveling when he first joined Better Call Saul season 3, which took place in 2003. With a goal of infiltrating the Salamanca family drug trade, he encountered Mike Ehrmantraut, another man with ties to the cartel. Gus hired him to essentially be his right-hand man and head of security. Through various flashbacks from Breaking Bad and Better Call Saul, a picture was pieced together of exactly how Gus became a crime boss. According to his stories, Gus hailed from Chile, where he grew up as a child in extreme poverty. Though there was no official record of Gus living in Chile, he eventually emigrated to Mexico before being granted a visa to the United States. It was his time in Mexico, however, that truly shaped his future.
In the '80s, Gus partnered with a chemist named Maximino Arciniega while living in Mexico. The pair decided to start a chain of fast food restaurants to cover their distribution of high-quality meth cooked up by Max. It's implied that they may have been more than just business partners, and that Gus and Max were actually in a romantic relationship. Either way, the duo proposed a deal with the Mexican cartel - specifically, Don Eladio Vuente. During the meeting, they unintentionally offended the powerful man, leading to Eladio ordering his henchman, Hector Salamanca to shoot Max in the head. This set up Gus' motivation for revenge against the Salamanca family, as seen in Better Call Saul.
Rather than act fast, Gus kept up with the business he and Max built, expanding Los Pollos Hermanos to the United States. He also established a chemistry scholarship at the University of New Mexico in his partner's name, and he was seen visiting a memorial dedicated to Max in Better Call Saul season 5. Gus eventually gets an opportunity with the cartel as a distributor leading up to the events of Better Call Saul. Despite the various reveals, questions still remain about the notion that Gus may have been a member of the military, and even had his own family. There was even a theory that Gus secretly worked for the CIA. Breaking Bad may have ended, but there's still another season of the prequel to fill in more blanks.