Swirly is a troublesome experiment, although very mute at that. He is quite active with his hypnosis, as it is performed at the most inadequate of times to humiliate others, but he is otherwise harmless. He often stares into space when not using his powers, being somewhat blank-minded.
Experiment 383 was the 383rd genetic experiment created by Jumba with Hämsterviel's funding. He was designed to hypnotize his victims into obeying the next order or suggestion they heard. 383 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, with 383's pod landing on a beach shore.
When a small wave washed over the shore, 383's pod got wet, activating the experiment. 383 then hypnotized a surfer, who had witnessed his activation, and left the scene.
After hypnotizing a tourist, 383 was discovered by Lilo and Stitch, but just before they could take action, Gantu ambushed them and captured 383 in a containment orb. 383 was soon caught in a fight between Lilo, Stitch and Gantu, which ended with Lilo and Stitch successfully retrieving 383.
Lilo and Stitch then took 383, named Swirly, back to their house, where they learned about his powers. They shortly after tried to hide Swirly from a strict Nani when she arrived home from work. However, in the ensuing chaos, Swirly managed to hypnotize both Lilo and Stitch and escape outside.
Gantu later recaptured Swirly and was briefly hypnotized by the latter back at his ship. Experiment 625 was fascinated by this and amused himself by making Gantu do silly stuff. Hämsterviel also became intrigued after seeing this, and toyed with Gantu a bit before snapping him out of his trance. Hämsterviel then told Gantu his clever scheme that involved using Swirly on the Look at This! show.
Later, Gantu arrived at the studio, where he used Swirly to hypnotize the manager into putting him on the Look at This! show. He then planned to have Swirly turn the show's viewers into slaves. Lilo and Stitch, who just so happened to be on the show, were still under Swirly's hypnosis from before.
Jumba, who was watching the show on TV back home, soon found out what was going on. He then came to the show in person and managed to snap Lilo and Stitch out of their trances so they could rescue Swirly.
Gantu attempted to hypnotize the show's viewers into slaves using Swirly, but Lilo and Stitch ultimately left Gantu holding the bag by recapturing Swirly. He was later found a once true place hypnotizing others at a children's party that Stitch had won from being on the show, with Mertle becoming one of Swirly's victims.
In "The Asteroid", Swirly was one of the six experiments that Stitch convinced to come with him and Lilo to save Earth from an approaching asteroid. Along the journey, Swirly hypnotized the extraterrestrial asteroid squatter to prevent him from distracting Lilo and the others as they safely diverted the asteroid using the ship's hyperdrive engine.
The first 624 experiments, including Swirly, 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.
Swirly participated in the following battle between the experiments and the Leroy clones by hypnotizing Leroys.
However, 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 failsafe.
Swirly made an appearance in the Stitch! anime where Hämsterviel used him to hypnotize Stitch into fighting for him. This episode also featured Plasmoid and Splodyhead who helped combat Stitch while he was hypnotized.
- When Swirly hypnotizes the Ice Cream Man, his eyes can be seen.
- Swirly's pod color is yellow.
- Swirly is described by the experiment computer screen as, "Experiment 383. Primary function: Hypnotizer. Makes victims susceptible to the first suggestion they hear."
- Swirly's head, antennae and ears appear in the online game Jumba's Lab.