Experiment 603 was the 603rd genetic experiment created by Jumba with Hämsterviel's funding. He was designed to be a living laser bolt. 603 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.
At an unknown point after this, Experiment 603 was activated.
In "627", 603 attacked a farm house, but was defeated when Stitch trapped him in a containment orb. However, Gantu and 627 arrived shortly after, and both managed to take 603 from an inattentive Stitch. 603, named Zap, was later seen multiple times flying around Gantu's ship.
The first 624 experiments, including Zap, were rounded 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.
Zap participated in the following battle between the experiments and the Leroy clones.
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 ʻOe", which caused the Leroy army to shut down due to the original Leroy's fail-safe.
- Zap's pod color is yellow.
- Zap is one of the few experiments to not appear in the group photo at the end of Leroy & Stitch.
- Zap appears to be physically similar to Pikachu, the mascot of the Pokémon franchise. Coincidentally, they both use electricity.