Experiment 288 was the 288th genetic experiment created by Jumba with Hämsterviel's funding. He was designed to act as a living boomerang. 288 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. Against statistically unlikely (but not impossible) odds, several experiment pods landed in one location: Mrs. Hasagawa's yard, 288's pod being one of them.
At an unknown point, Mrs. Hasagawa mistook 288's for an apricot and washed it, activating the experiment. However, as 288 was not a very evil or destructive experiment, he was able to live a peaceful life with her, due to the latter seeing the former as a mere stray cat who needed a home.
When Lilo and Stitch discovered that Mrs. Hasagawa kept several experiments as pets, they thought they were a danger to her and along with Jumba and Pleakley, tried to capture them all. Stitch tried to get 288 to willingly go into a container, but when he saw Experiment 111 rapidly approaching, he grabbed 288, threw him into the air, and used the aforementioned container on 111 instead. When 288 came back (the way real boomerangs do after being thrown), Stitch grabbed another container and caught him in it.
288 and the other experiments were about to be taken away, but were returned to Mrs. Hasagawa when Lilo and Stitch saw how much she cared for them. 288 was then named Boomer.
In "Woops", Boomer was oddly seen as one of the captive experiments in Hämsterviel's prison cell, although he is barely seen, suggesting Gantu caught Boomer, but this was an error. Boomer was then sent back to Gantu after Experiment 600 caused mischief and nearly blew Hämsterviel's cover to the prison guards.
The first 624 experiments, including Boomer, 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.
Boomer participated in the following battle between the experiments and the Leroy clones by being thrown at Leroys' heads.
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.
- Boomer was activated off-screen.
- In "Woops", Boomer erroneously appeared with Gantu's other captive experiments, although he is barely seen, but he was already living with Mrs. Hasagawa, and Lilo and Stitch discovered him while Gantu was asleep.