4-LOM was an ambitious protocol droid who overwrote his own programming in order to embark on a life of crime. A LOM-series droid, 4-LOM's first assignment was aboard a luxury liner named the Kuari Princess, where he served as a translator between the vessel's wealthy passengers and its computer. He found this work to be mundane and undemanding, and after the Kuari Princess's computer altered his programming, 4-LOM began to steal from the passengers. Eventually, he left the Kuari Princess for good, becoming an expert thief, information broker, and, after Jabba Desilijic Tiure altered his programming further, a highly-successful bounty hunter.

Jabba paired 4-LOM with another hunter named Zuckuss, and together they claimed several high-profile bounties for the Hutt Cartel. Although 4-LOM had initially only partnered with Zuckuss in order to learn the Gand's intuitive findsman abilities, the two bonded, and the droid stayed loyal to Zuckuss after the Gand was critically injured during the Galactic Civil War. Desperate for the funds necessary to heal Zuckuss, the pair incurred the wrath of the Galactic Empire when they accepted a bounty on Nardix, an Imperial governor. However, Darth Vader ignored this fact when he enlisted their aid during the hunt for Han Solo. 4-LOM and Zuckuss conspired to infiltrate the Rebel Alliance, hoping to kidnap Solo at the Rebel rendezvous point, though Boba Fett managed to capture the bounty before them.

After the Rebels healed Zuckuss, the two bounty hunters joined the Alliance and attempted to rescue Han Solo from Boba Fett before the Mandalorian could deliver him to Jabba the Hutt. They failed utterly, though, and 4-LOM was left badly damaged. Zuckuss restored him, but had to perform a complete memory wipe to do so; the idealism that led the droid to join the Rebellion was gone, and 4-LOM no longer remembered his aspirations of achieving intuition and mastering the Force. He became a cold, calculating individual, and took bounties from unsavory employers such as Quaffug—he also left the Rebel Alliance and severed ties with Zuckuss. The two did perform one last hunt together, capturing Drawmas Sma'Da for a sizable sum of money, though from that point on, 4-LOM worked alone.