Gigi

Gigi, A.K.A. "Yapper" and Experiment 007, is an illegal genetic experiment created by Jumba Jookiba. She is designed to annoy Jumba's neighbors with her constant yapping. Her one true place is with Mertle Edmonds. Gigi's voice consists of two actors, Frank Welker (vocal noises) and Tress MacNeille (speaking voice).

Bio
Experiment 007 was the 7th genetic experiment created by Jumba with Hämsterviel's funding. She was designed to sit, fetch and annoy Jumba's neighbours with her constant yapping.

007 and the other first 624 experiments were deactivated and smuggled to Earth by Jumba during his mission to capture Experiment 626.

All of the experiment pods were released and scattered across the island of Kauai.

Lilo & Stitch: The Series
At an unknown point, Experiment 007 was activated and found and named Gigi by Mertle.

Mertle showed Gigi off to Lilo and Stitch, but when Gigi's yapping began to annoy Stitch, the latter swallowed her whole, before Mertle dragged her out of Stitch's stomach and took her to a pet salon to get cleaned up.

Later, Mertle took Gigi with her to Honolulu to compete against Stitch in a dog competition.

Gigi won through Mertle cheating, but at that moment, Gantu arrived to take Gigi. However, before Gantu could escape with her, Stitch was able to defeat the former. When Lilo saw how much Mertle truly cared for Gigi, the former decided to leave Gigi with Mertle.

Gigi reappeared in "Amnesio", being walked by Mertle and the hula girls.

Leroy & Stitch
Gigi was seen being walked by Mertle, the latter stopping to taunt Lilo before moving on.

Later, the first 624 experiments, including Gigi along with Mertle, were round up by Leroy and taken to a stadium to be destroyed. However, Lilo, Stitch, Jumba, Pleakley, Reuben and Gantu arrived before the experiments could be destroyed.

During the following battle between the experiments and the Leroy clones, Mertle with Gigi tried to avoid attacking Leroys. When Mertle and Gigi were saved from a Leroy by Clip, Gigi revealed her ability to speak and her status as an experiment, then pushed Mertle out of the way of a Leroy's plasma blast.

The Leroys soon gained the upper hand in the battle, but were defeated when Lilo, Stitch, Reuben and several other experiments performed the song Aloha Oe, which caused the Leroy army to shut down due to the original Leroy's failsafe.

Following the battle, Gigi declared that she wanted to be part of Lilo's ohana, prompting Mertle to join it with Gigi.

Trivia

 * Gigi did not speak in the Lilo & Stitch TV series. However, in the movie Leroy & Stitch, it was revealed that she could actually talk and says, "Nice one, cousin." She then says, "Look out!" and pushes Mertle out of the way of an incoming plasma blast.