Swapper

Swapper, A.K.A. Experiment 355, is an illegal genetic experiment created by Jumba Jookiba. He is designed to switch people's minds. His one true place is in the hospital doing brain surgery. Swapper is voiced by Frank Welker.

Lilo & Stitch: The Series
Experiment 355 was the 355th genetic experiment created by Jumba with Hämsterviel's funding. He was designed to swap any two (or more) individuals' minds. According to Jumba, 355 once swapped the former and his wife for an entire month. 355 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 355 was activated and captured by Gantu.

When Gantu was about to send 355 to Hämsterviel, 355 got loose and swapped Gantu and Hämsterviel's minds, allowing 355 to escape.

Hämsterviel in Gantu's body then decided to go AWOL and recapture 355, but refused to have 355 switch their minds back, although Gantu in Hämsterviel's body protested.

Sometime later, Lilo and Stitch encountered 355 and managed to capture him, but 355 was able to swap their minds in the process.

When 355, named Swapper, refused to switch Lilo and Stitch's minds back, they took him back to their home, where Jumba covered up Swapper's container with a towel to prevent the experiment from using his mind-swapping power on the former.

When Pleakley removed the towel, Swapper switched his and Jumba's minds as well, forcing Lilo's dysfunctional ohana to throw a sensible party that she hosted earlier (to prove she wasn't weird), after Victoria, Mertle and the hula girls arrived.

Later, Hämsterviel in Gantu's body arrived at the Pelekais' house for Swapper, and a fight ensued during which Swapper swapped Lilo, Stitch, Jumba and Pleakley's minds again, though into someone else's body this time.

After Hämsterviel in Gantu's body was defeated, Swapper switched Lilo, Stitch, Jumba and Pleakley's minds back into their original bodies, and was then forced to switch Gantu and Hämsterviel back into their original bodies under the threat of being given Pleakley's disgusting food for dinner.

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

Swapper 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. Swapper joins them for the song by playing the keyboard.

Stitch! anime
Swapper made an appearance in the Stitch! anime where he used his powers on Stitch and Hiroman. Until they could find Swapper again, Hiroman needed to figure out how to use Stitch's abilities to take on Heat. After Heat, Gantu and Reuben were defeated, Jumba made a request for Swapper to swap Stitch and Hiroman back into their original bodies, but he instead swapped everyone's bodies again!

Trivia

 * Swapper's pod color is blue.
 * Swapper is described by the experiment computer screen as, "Experiment 355 Primary function: Swaps people's minds."