Wikisimpsons - The Simpsons Wiki
Before Gabbo's show premiered, numerous advertisements mentioning him were posted on TV and in the streets. The town was abuzz with anticipation, with everyone eager to find out who (or what) Gabbo was.
Gabbo's TV show then began, airing opposite Krusty the Clown, and was an instant hit. A colorful, vivacious puppet (even by the standards of Springfield), he was offset by his more rigid and refined puppeteer, Arthur Crandall, and the combination was very successful. They were so successful, in fact, that they became more popular than Krusty for a brief time, forcing his show into cancellation.
In an effort to bail out his idol, Bart Simpson snuck into the studio where Gabbo's show was being filmed. During a commercial break, Bart caught Gabbo badmouthing his fan base—the children of Springfield—in spite of Arthur Crandall's urgings for him to relent. Bart switched the camera back onto the air before the commercial break was over, broadcasting Gabbo uttering the words, "All the kids in Springfield are S.O.B.s." Despite this, Gabbo was still number one, according to a newspaper headline the next day.
Following Gabbo's gaffe, Krusty (with the aid of Bart and Lisa) launched a spectacular comeback special which included a number of his celebrity friends. The special was a huge success and re-established Krusty's stranglehold on the hearts of the children of Springfield.
Arthur Crandall and Gabbo were later hired as part of an act for the Native American Casino. Gabbo had noticeably deteriorated from wear and tear with the passage of time, and was also shown as simply being a dummy when not in use.
When the EPA trapped Springfield in a dome during Trappuccino, Gabbo's jaws comically fell off as he (along with the rest of the townspeople) gaped in surprise at the sight of the dome moving into position and then being lowered.
 Behind the Laughter