Topper

Topper, A.K.A. Experiment 025, is an illegal genetic experiment that was created by Jumba Jookiba. He is designed to give off a bright light with which to pose as an invasion-signaling beacon to the Galactic Armada. His one true place is as a Christmas star.

Lilo & Stitch: The Series
Experiment 025 was the 25th genetic experiment created by Jumba with Hämsterviel's funding. He was designed to use his bright light to pose as a beacon for an invasion to the Galactic Armada. 025 and the other first 624 experiments were deactivated and smuggled to Earth by Jumba during his mission to capture Experiment 626.

025's pod was found by Gantu on Christmas Eve and intended to be sent as a Christmas present meant for Hämsterviel, though Experiment 625 advised Gantu to get the pod giftwrapped first.

Meanwhile, Lilo was trying to teach Stitch about Christmas when the latter suddenly noticed a woman giftwrapping 025's pod. Stitch hastily swiped what he thought was the gift with the experiment pod, but when he tried to tell Lilo, she ignored him.

When Gantu arrived to pick up 025's pod, the same woman who had wrapped it hinted that there was a mishap involving Stitch, much to Gantu's anger. He then swore that he would avenge Stitch for stealing the gift prepared for Hämsterviel.

In an attempt to find the pod, Stitch stole countless presents from every house and the local mall. Lilo assumed Stitch was selfishly hoarding gifts for himself, but after Stitch was captured and interrogated, he revealed to everyone what he was really trying to do. Shortly after, Gantu attacked the house and made off with all the presents that Stitch had stolen.

When Lilo, Stitch, Jumba and Pleakley pinpointed the experiment pod in town, the four tussled with Gantu dressed in a Santa outfit. Lilo and Stitch liberated the giftwrapped pod from Gantu, though he retrieved it after a long chase. However, when Gantu attempted to crush Lilo for meddling, the latter reprimanded him, only to learn that he planned to give 025's pod to Hämsterviel as a Christmas present.

Just then, a little girl asked Gantu for a mere Christmas gift, believing he was actually Santa. Forced to comply, Gantu ended up giving 025's pod to her and later distributed presents to other children, thereby honoring the true spirit of Christmas.

After Jumba discovered 025 to be harmless, Lilo activated 025 in a fountain. She then named him Topper and, after sharing him with the little girl from before, gave him a one true place atop the local Christmas tree (actually a decorated Pleakley) as a Christmas star, while Topper's bright light unintentionally signaled the Galactic Armada.

Topper reappeared in "Elastico" as one of the audience for Lilo's hula dance.

The Origin of Stitch
Topper was one of the experiments that was gliding on the screen, but he is 591 instead of 025.

Leroy & Stitch
The first 624 experiments, including Topper, 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.

Topper 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 fail-safe.

Stitch! anime
Topper made a cameo appearance in the Stitch! anime as one of the experiments in Hämsterviel's prison cell.

Trivia

 * Topper's primary function is to use his bright light to signal the alien attack fleet. However, on the Disney site, it is incorrectly stated that Topper's light is designed to keep people awake.
 * Even though Topper was found a one true place on a Christmas tree, it is unknown what he does during the other seasons.
 * Topper's pod color is white.
 * Topper is described by the experiment computer screen as, "Experiment 025 Primary function: Keeper of awakeness to people."
 * His number is likely a reference to Christmas Day (December 25).