Gaila was a Ferengi arms dealer who was successful enough to buy his own moon. Odo noted that he knew Gaila to be a more devious Ferengi than Quark, his cousin. (DS9: "Civil Defense", "The Way of the Warrior")
In 2372, during a discussion between Quark and Garak over Quark's surplus of kanar in storage due to the lack of Cardassian customers, Quark regrettably remarks that he should have listened to his cousin Gaila in entering the arms market with him. In retrospect, Quark admits that no one ever went broke selling weapons, but nonetheless didn't listen to Gaila's advice because he was a "people person"; that he enjoyed interacting with his customers as opposed to the impersonal nature of arms customers. (DS9: "The Way of the Warrior")
In 2362, Quark loaned Gaila the latinum to start a munitions consortium, and in return, Gaila promised to buy Quark a ship if he became successful. Gaila finally appeared to honor his debt in 2372 when he sent Quark a Ferengi shuttle, which Quark designated Quark's Treasure. The shuttle was later found to have been sabotaged in a failed attempt by Gaila to kill Quark. (DS9: "Little Green Men")
Later that year, Quark planned to use the money generated from the sale of his vacuum desiccated remains to pay back Gaila. After he learned he did not have Dorek Syndrome, Quark tried to rescind the debt payments. (DS9: "Body Parts")
In 2373, Gaila and his business partner Hagath approached Quark to make use of his holosuites for use in their business endeavors. Though Gaila and Hagath had no qualms about selling weapons that would be used to kill millions of people, Quark began to have a crisis of conscience, particularly after learning the Regent of Palamar intended to buy biogenic weapons that would be used to that effect.
Quark eventually double-crossed Gaila and Hagath by arranging for the Regent's enemy, General Nassuc to come to the station and "accidentally" run into them. Following the ensuing firefight, Gaila and Hagath fled the station with the Palamarian Freedom Brigade's purification squads in pursuit. (DS9: "Business as Usual")
Gaila managed to evade the purification squads but soon fell on hard times. In 2374, Gaila was arrested on Thalos VI for vagrancy. He had a fine levied against him, but was unable to pay it and ended up in prison. Initially swearing revenge against Quark, his vengeance soon gave way to greed after learning about an offer to earn latinum by joining Quark's team to rescue his mother Ishka, who had been captured by the Dominion. He accepted the offer when he learned that Quark paid his fine.
Gaila insisted that he was "a weapons dealer, not a soldier" and proved to be all too right as he jeopardized the mission more than once. First, he nearly allowed Keevan, the Vorta prisoner to be exchanged for Ishka, to escape when he fell asleep while guarding him. Later, after discovering that Quark intended to keep most of the reward money for himself, Gaila attempted to shoot him but shot and killed Keevan instead.
Gaila makes an appearance in the Deep Space Nine relaunch novel Demons of Air and Darkness. He and his cousin, Quark, are on the opposite side of a negotiating table involving supposed Iconians and the Orion Syndicate.