Dupe is shown to be fun-loving, childish and immature, due to the fact that he was programmed to be one of the younger experiments (along with Mr. Stenchy and Babyfier). Because of this, he is often treated as the baby of the heroes' side, as his cloning powers are neither chaotic nor destructive. He is also playful, friendly and optimistic.
Experiment 344 was the 344th genetic experiment created by Jumba with Hämsterviel's funding. He was designed to use his clone-generating ability to clone single individuals into entire armies, but all of the original's traits were divided between them and the clones. 344 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 344 was activated.
After Jumba explained 344's powers, the latter demonstrated them by duplicating a lollipop and then a birthday cake.
The following night, after Mertle and the hula girls did not attend Lilo's slumber party that she hosted earlier, Lilo used 344, christened Dupe, to generate clones of herself that she could befriend. However, Stitch hastily intervened, resulting in him being cloned into four instead.
Later that night, Gantu, 033, 609, 544 and 617 attacked the Pelekai residence. The Stitch clones tried to fight back, but due to a side effect from Dupe's replication, they had all become very weak, thus enabling Gantu and his henchmen experiments to easily defeat and capture all four Stitches in containment orbs.
Shortly after Stitch was kidnapped, Lilo hatched a plan and used Dupe to generate three clones of Pleakley, leaving the original comatose. Lilo and the Pleakley clones then launched a rescue mission on Gantu's ship while taking Dupe with them so he could re-merge the Stitch clones.
When Gantu noticed them and Lilo notified him of Dupe's cloning powers, Gantu grabbed Dupe and cloned Hammerface, Heat, Thresher and Plasmoid each into a hundred replicas. However, as a result of being tricked by Lilo, the experiments had all become complete weaklings, and thus were easily defeated by Lilo and the Pleakleys.
Lilo then used Dupe to re-merge the freed Stitch clones into the original, and Lilo, Stitch, Dupe and the Pleakley clones escaped the ship.
Dupe then re-merged the Pleakley clones into the original, and was later found a one true place making half-calorie Shave Ice.
In "Remmy", Dupe was one of the experiments in Lilo's dream.
In "Snafu", Slushy and Dupe were seen using their combined powers to sell multiple Shave Ice cones, which a couple bought and enjoyed. Gantu then attempted to revert the rehabilitated experiments to evil by playing a recording of Angel's song, but due to interference from Experiment 120, Gantu's karaoke tape was played instead, much to Slushy and Dupe's humor.
The first 624 experiments, including Dupe, 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.
Dupe participated in the following battle between the experiments and the Leroy clones by splitting attacking Leroys into weakling 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 fail-safe.
Dupe made an appearance in the Stitch! anime where his tweak was altered by Hämsterviel, so instead of making things weaker once duplicated, the duplicates are made stronger than the original, rather than the other way around.
- Dupe's pod color is yellow.
- Dupe is described by the experiment computer screen as, "Experiment 344. Primary function: Duplication."
- Dupe's antenna and ears appear in the online game Jumba's Lab.
- Dupe appears in the online game Lilo & Stitch: Alien Interception along with Plasmoid, Tank, Clyde, Yang and Hämsterviel.