Pallomari was the main accountant for the Cali Cartel, which meant that he was in charge of sending money to the corrupt police officers and managing how much money the cartel had at all times.
The first time Pallomari was introduced was in The Kingpin Strategy (3x1). He was shown helping Miguel Rodriguez-Orejuela with payments. The next time we see Pallomari is when Javi Pena shows up at one of the cartel's offices to do a search. Pallomari was warned by Jorge Salcedo, an important figure to the cartel's security, but did not believe him. Luckily, Jorge was able to get inside the building and hide all of the money that Pallomari was counting at the time.
After that incident, Jorge hides Pallomari and his family, two sons and his wife, in one of the cartel's safe houses. It was a small apartment, which the family complained about, but had to deal with in order to stay alive. Patricia, his wife, has been having an affair with her colleague, Freddy Moya. The two claim to "be in love with each other." Having their suspicions about their safety, Pallomari and his family move themselves to another part of the country. This greatly upsets David, Miguel's son, who is supposed to find Pallomari and kill him. The only person that knows about the Pallomaris' location is Freddy, who calls Patricia frequently. Towards the end of the season, Freddy goes to see David and give Guillermo Pallomari's location to have Patricia to himself a nd to receive the cash reward for giving up Pallomari. However, David tortures Freddy to find out where Guillermo is. When he finds out, David tries to go to his car but is gunned down by the North Valley Catel.