Link

Link, A.K.A. Experiment 251, is an illegal genetic experiment created by Jumba Jookiba. He is designed to stick squabbling people together so that their arguing causes mass chaos. The putty used to bind them is extremely durable, and practically indestructible; the only thing that can make it dissolve is mud. His one true place is working at the Bungee Diving for Couples, not only creating a fun ride, but also teaching arguing couples to do things together. Link is voiced by Frank Welker.

Bio
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. Thus, the two's squabbling and attempts 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 in the sand on a beach.

Lilo & Stitch: The Series
While Lilo and Mertle were digging for buried treasure on the beach, Mertle accidentally shoveled 251's pod into the path of an incoming wave, activating the experiment.

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

251 attacked the Pelekai household next. When Jumba and Pleakley argued over the messy lab incident, 251 stuck them together as well. He then stuck Stitch and Nani together when the former tried to drag Nani off, wanting her to help with Lilo's sticky situation.

Consequently, Nani was forced to take a reluctant Stitch along with her on a water skiing trip, despite Stitch's hatred of water.

During the boat drive, a thrilling series of events took place, including the boat's engine stalling and Stitch hot-wiring the boat to start it up again. In the end, the boat skidded onto the beach and threw Nani and Stitch in the mud, which dissolved the sticky substance, much to their relief.

Later, Stitch unstuck Jumba and Pleakley by throwing a bucket of mud over their bonded area.

Meanwhile, 251 went on a rampage around town, sticking arguing pairs together. Lilo and Mertle chased 251 through the streets of Kokaua Town, then ended the chase when they used the goo binding them to lasso 251 into Lilo's backpack. Lilo decided to name 251 Link, which didn't interest Mertle.

Gantu then showed up and demanded the experiment (as well as their treasure map). Link escaped Lilo's backpack, while Gantu, Lilo and Mertle chased after him. Eventually, Lilo and Mertle 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 ambushed and captured by Gantu, who took Link back to his ship with Lilo and Mertle still stuck to his head. Fortunately, Stitch came to the rescue with more mud and separated them all. After Link was freed, he stuck Gantu and Experiment 625 together.

Lilo, Stitch and Mertle then managed to escape the ship with Link, who 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 Oe, which caused the Leroy army to shut down due to the original Leroy's failsafe.

Stitch! anime
Link made an appearance in Season 2 of the Stitch! anime along with Hammerface, Babyfier, Spike, and Woody. He used his powers to stick Yuna together with her rival.

Trivia

 * Link resembles a yellow Grundo.
 * It is believed that Experiment 251 is named Link because he links people together. However, according to Lilo, it's short for Linkenstein (the zombie president).
 * Link is one of Stitch's few cousins to have red eyes instead of black ones like the rest.
 * Link's pod color is green.
 * In the anime episode "Link-age," Reuben states that Link's favorite type of sandwich is reverse hot dogs.