Link

Link, A.K.A. Experiment 251 and Linkenstein, is an illegal genetic experiment created by Jumba Jookiba. He is designed to pinpoint and stick squabbling people together with a super-sticky adhesive from his antennae so that their arguing causes massive chaos. The glue used on them is elastic, highly durable, and nearly indestructible; the only thing that can make it dissolve is mud. His one true place is working at the Cliff Diving for Couples attraction, teaching arguing couples to do things together by bungee jumping.

Lilo & Stitch: The Series
Experiment 251 was the 251st genetic experiment created by Jumba with Hämsterviel's funding. He was designed to hunt down and stick squabbling individuals together with near-indestructible goo from his antennae. Thus, the pair's arguing and efforts to pull away from each other would result in chaos and destruction. 251 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, with 251's pod landing embedded in the sand on a beach.

While Lilo and Mertle were digging for buried treasure on the beach, Mertle accidentally shoveled 251's pod into the path of an incoming tide, activating the experiment.

When Lilo and Mertle began arguing over a treasure map they both found, 251 stuck them together with a sticky blue substance and ran off in search of trouble. Unable to break free from each other (even after Stitch attempted to separate them), Lilo told Stitch to go back for help.

251 attacked the Pelekai residence next. When Jumba and Pleakley bickered over a messy lab incident, 251 stuck them together as well. He then stuck Stitch and Nani together (thinking they were arguing) when the former tried to drag Nani off, wanting her to help with Lilo's sticky situation.

Nani was then forced to take a reluctant Stitch with her on a water skiing trip, despite Stitch's hatred of water. While Nani drove the boat, a series of thrilling events occurred, such as the motor stalling and Stitch hot-wiring the boat to restart the engine. In the aftermath, the boat skidded onto shore and threw Nani and Stitch in the mud, which dissolved 251's glue, much to their relief.

Sometime later, Stitch and Nani returned to the house to discover Jumba and Pleakley intending to use a laser machine to unstick themselves. However, Stitch unstuck them by throwing a bucket of mud over their bonded area.

Meanwhile, 251 went on a rampage around Kokaua Town, sticking quarreling pairs together with his highly effective adhesive. Shortly after, Lilo and Mertle chased 251 through the streets of town, then ended the chase when they used the goo that was binding them to lasso 251 into Lilo's backpack. She decided to name 251 Link, which didn't interest Mertle.

Lilo and Mertle then resumed their conflict until Gantu showed up and demanded the experiment (as well as their treasure map). In the commotion, Link escaped Lilo's backpack, while Gantu, Lilo and Mertle chased after him. Eventually, the trio cornered Link, but the latter escaped by sticking Lilo and Mertle to Gantu's head.

Link later attacked a golf course, where he targeted two arguing golfers. However, he was blasted into a net by Gantu, who took Link back to his ship with Lilo and Mertle still stuck to his head. Fortunately, Stitch soon arrived with more mud and separated them all. After Stitch freed Link, the latter stuck Gantu and Experiment 625 together, allowing Lilo, Stitch and Mertle to escape the ship with Link.

Link was later found a one true place teaching arguing couples to do things together by helping them bungee-jump off a cliff diving attraction.

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

Link 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 ʻOe", which caused the Leroy army to shut down due to the original Leroy's fail-safe.

Stitch! anime
Link made an appearance in Season 2 of the Stitch! anime along with Hammerface, Babyfier, Spike, and Woody. It is revealed that Hämsterviel reverted these experiments to evil using a recording of Angel's song, thus enabling them to wreak havoc on the island. Link used his powers to stick Yuna together with her rival.

Trivia

 * Link resembles a yellow Grundo from the  universe.
 * According to Lilo, she named 251 "Link" not because he links people together, but because it is short for Linkenstein (the zombie president).
 * Link is one of the rare experiments to have red eyes instead of black ones like most of the rest.
 * Link's pod color is green.
 * Link is described by the experiment computer screen as, "Experiment 251. Primary function: Links squabbling pairs together."
 * In the English dub of the Stitch! anime episode "Link-age", Reuben states that Link's favorite type of sandwich is reverse hot dogs.