Although Heckler acts like a jerk most of the time, he really just seems to insult out of impulse. He cannot help but make fun of others, but has been proven to be willing to help people, especially when it comes to insult comedy. Most of the time, he does not entirely intend to offend others, but it is in his programming, and he cannot help but throw around a few insults. If not, he breaks down into a fit of self-pity, as he never had any other purpose.
Heckler has the ability to be kind-hearted, but just has a very strange way of showing it. He loves his job being in the dunk tank and encouraging people to try to dunk him for charity, smiling good-naturedly right before Mertle dunked him. When he insults someone, it can be hard to tell if it is out of reflex, just teasing, or actually trying to be hurtful.
Experiment 322 was the 322nd genetic experiment created by Jumba with Hämsterviel's funding. He was designed to undermine enemies by verbally insulting their appearance and personality. 322 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.
Experiment 322 was activated off-screen at the Birds of Paradise Hotel, where he then impressed a crowd of tourists by insulting the tour guide's hair and shirt, earning 322 a round of applause from the crowd.
322 was later chased around town by Gantu, but the former was able to stay ahead by repeatedly insulting Gantu until 322 was soon rescued by Lilo and Stitch. When 322 antagonized Stitch, the latter attempted to beat him up, only to be stopped by Lilo, who considered 322 useful.
Lilo and Stitch shortly after took Heckler back to their house, where the latter insulted their dwelling and also both Nani and Jumba. When Jumba tried to silence Heckler by stuffing Stitch into his mouth, the latter spit Stitch out and insulted how he tasted, which led to them tussling on the floor.
Later, Lilo and Stitch looked to Heckler for guidance for Pleakley's stand-up comedy at Nani's charity event, and Heckler convinced them to give the audience rotten tomatoes to throw at Pleakley's rotten jokes. Although uncertain, Lilo and Stitch took Heckler's advice (unaware that he was leading them astray).
At Nani's charity event, Heckler's insults towards the staff caused all of them to quit. When Nani then demanded Lilo to get rid of Heckler, the latter insulted Lilo's voice and nose before attempting to escape. Gantu then barged in for Heckler, though Nani, Lilo and Stitch, sick of Heckler's verbal abuse, gladly handed him over.
Thus, Heckler returned to Nani's charity event, where he was soon after chased by Stitch. While being pursued, Heckler caused massive chaos at the dining tables by kicking and throwing food at people, including Nani.
Heckler then threw a rotten tomato at one of Pleakley's jokes, and went onstage to insult him in front of everyone. At that moment, however, Pleakley and Lilo (as well as the entire audience) accepted that Heckler's insults towards them were true, leaving him defeated and sobbing on the stage.
After Lilo managed to console Heckler, she found his one true place in a dunk tank, where he provoked people to try and dunk him, especially a vengeful Mertle.
The first 624 experiments, including Heckler, 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.
Heckler participated in the following battle between the experiments and the Leroy clones, but it is unknown what he did. He probably agitated Leroys with his verbal abuse.
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.
- Heckler was possibly inspired by Don Rickles, a comedian who was known for insulting people for humorous effect.
- Like Reuben, Heckler is one of the very few known experiments that can speak English rather fluently.
- Heckler's pod color is red.
- Heckler is described by the experiment computer screen as, "Experiment 322. Primary function: Bully. Undermine enemy morale with verbal abuse."
- Oddly, when Heckler's image is reflected off of Stitch's eyes in The Origin of Stitch, he is gagged and handcuffed for some reason.
- Heckler is one of the few experiments to not appear in the group photo at the end of Leroy & Stitch.