Heat

 Heat, A.K.A. Experiment 609, is an illegal genetic experiment created by Jumba Jookiba. He is designed to shoot explosive fireballs from his forehead. He was captured by Gantu, but was rescued in "Snafu." His one true place is as Melty's assistant at the recycling plant. Heat is voiced by Dionne Quan.

Bio
Experiment 609 was the 609th genetic experiment created by Jumba with Hämsterviel's funding. He was designed to fire explosive fireballs from the large bulb on his forehead.

609 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.

Lilo & Stitch: The Series
609's pod eventually made its way to a junk shop, where it, along with 544, 617 and 033, was stolen by Gantu, activated, and named Heat in "Dupe."

Plasmoid, Heat, Thresher and Hammerface were then led by Gantu in an attack on the Pelekais' house, where Heat and the other three experiments were able to easily defeat and capture Stitch and his replicas.

The five returned to Gantu's ship for a victory feast, but were interrupted by Lilo, Pleakley and Dupe. Gantu used Dupe to clone Heat into a hundred replicas, but as Heat's power was thus divided between them, they were complete weaklings.

It is presumed that Hämsterviel was somehow able to re-merge the weakling Heats into one.

Heat reappeared in "Snafu," and was freed along with Gantu's other captive experiments by Lilo, Stitch, and several other experiments in a rescue mission.

Leroy & Stitch
The first 624 experiments, including Heat, were round 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.

Heat 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 `Oe, which caused the Leroy army to shut down due to the original Leroy's failsafe.

Stitch! anime
Heat made an appearance in a later episode of the Stitch! anime along with Swapper. Swapper switched Stitch's and a local school boy's bodies. Then, when Heat attacked, the child required to figure out how to use Stitch's abilities to win.

Trivia

 * Heat's pod color is green.
 * Heat is described by the experiment computer screen that says "Experiment 609 Primary function: Heat exploder."