Gastro is a terror bird who appears in The Terror-Bird Trap as the benevolent leader of Queen Soapi's avian assistants. He and his friends Gordon, Godfrey, Gideon, Gary, and Gus were chased off of Terra Nesta because they refused to act like terror birds, becoming plumbers and vegetarians. They fled, but their ship crashed on Atlantos and they were adopted by the native bactrosaurs, who they gave plumbing to in exchange for a place to stay.
He first met Teggs when he mistook the astrosaurs for megalodon spies, but Soapi and her hoof-maiden Janice interrupted the "fight", and Gastro apologized for jumping to conclusions. He was always willing to help his friends any way he could, even carrying Janice to safety after she fainted for the umpteenth time. Gastro also invented Spotless Survival Suits so that they would be safe even if Kleen Island completely sank. However, Janice was really a traitor and goaded the other terror birds into betraying Gastro, having them break his pipes and sabotage his Survival Suits. Teggs, misinterpreting the evidence, thought that Gastro was the villain who was faking cave attacks to upset Soapi while polluting the sea to anger King Fin the megalodon. The war between the two species began, but it didn't last long, for the combination of sabotaged weapony and the megs' tank-tanks immobilized both sides.
Janice revealed her true nature and captured Soapi, calling Gastro a dummy. Gipsy burst out of Gordon's megalodon costume and attacked the evil terror birds. Gastro helped Teggs defeat a trio of the feathered traitors, taking down Godfrey, and asked where Janice had gone. Seeing her, Arx trapped her using guns taken from a broken tank-tank. Gastro then helped the bactrosaurs save the megs and take them to the sea. He told them that he'd make a mixture that would clean up the water. Iggy offered to help him fix the toilets, and Soapi told him that he could live on Kleen Island permanently.
- Gastro is probably a Titanis, a type of gigantic, flightless, and predatory bird from the early Cenezoic era.
- Unlike most of the other terror birds, Gastro has thick black stripes on his tail.
- Real terror birds were obligate carnivores, meaning Gastro would have to meat since he cannot digest plant matter.