Gallico worked the drug trade in San Francisco. When Bob Glover needed to buy heroin in large quantities for Jesus DeSade, he went to Gallico. When the deal went sour, Gallico came looking for Glover in his office.
He didn't find him. He did, however, meet Jesse Custer and Cassidy, who were hunting for Glover after the death by overdose of Cassidy's girlfriend. They beat up Gallico and tortured him for information, which he gave them.
Cassidy and Custer left, but were soon replaced by Starr and Hoover, members of The Grail who were looking for Custer. Starr was also looking to kill Glover because of a mistake involving back-alley sodomy.
Gallico tried to take a shot at Starr, but was himself shot and killed by Hoover.