Experiment 628 is an illegal genetic experiment created by Jumba Jookiba, and the second experiment to be created on Earth with limited alien technology. It was created shortly after Experiment 627. After Stitch defeated 627, Jumba locked 628's pod away in a vault.
Experiment 628 was the 628th genetic experiment created by Jumba, and the third to be made without Hämsterviel's funding. Its purpose is unknown, as it is only ever seen in pod form.
In promotional material for Leroy & Stitch, Leroy was referred to as Experiment 628. However, this is false as he was only called Leroy in the film and is the evil doppelganger of Experiment 626.