Experiment 544 was the 544th genetic experiment created by Jumba with Hämsterviel's funding. He was designed to smash up crops with his mace-like tentacles, although he can also use them to attack and battle enemies. 544 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.
Back at his ship, Gantu trained and conditioned Hammerface, Heat, Thresher, and Plasmoid by using Experiment 625 for target practice, much to his indignity. The four henchmen experiments were then led by Gantu in an attack on the Pelekais' house, where their boss ordered them to defeat and capture Stitch and his replicas after seeing that he had been split into four.
Thresher engaged one of the clones in a duel. The clone picked up a broom and started spinning it similar to a bo staff. While he did this in front of Thresher, the latter appeared to be mesmerized, but stretched out one of his mace-tipped tentacles and poked the clone in the shoulder. When the clone turned his head, Thresher aimed another tentacle at his victim's face. Pleakley, seeing Thresher's plan, tried to warn the clone but was too late, as Thresher managed to knock him unconscious. The slug-like experiment then used his long tentacles to pick up his defeated opponent and place him in one of Gantu's containment orbs.
After capturing Stitch and his duplicates, the five returned to Gantu's ship for a victory feast (courtesy of Reuben), but were interrupted by Lilo, Pleakley, and Dupe. After Lilo tricked Gantu into using Dupe's cloning ability, Gantu used Dupe to clone Thresher into a hundred replicas. However, as Thresher's power was divided between them, they all became complete weaklings, and thus were easily defeated.
Presumably after this, they were all sent to Hämsterviel who was somehow able to re-merge the weakling Thresher clones into the original.
In "Remmy", Thresher was one of the experiments in Lilo's dream.
Thresher reappeared in "Snafu", and was freed along with Gantu's other captive experiments by Lilo, Stitch, and several other experiments in a rescue mission.
The first 624 experiments, including Thresher, 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.
Thresher participated in the following battle between the experiments and the Leroy clones. During the climax, when Stitch points to the stage in the stadium, Thresher can be seen bonking a Leroy clone on the head.
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 fail-safe. Thresher joins them for the song by playing the marimba.
- Thresher is one of the ten known experiments named by someone other than Lilo, the other nine being Gigi, Elastico, Yaarp, Hammerface, Heat, Plasmoid, Morpholomew, Shrink, and Leroy.
- Some sources have spelled this experiment's name as "Thrasher," but "Thresher" is the correct spelling.
- Thresher's pod color is purple.