Lilo & Stitch is one of the Disney Animated Canon's most unconventional franchises, having been going along its own path since Chris Sanders and Dean DeBlois made the 2002 original film. This has led it to become an Ensemble Dark Horse unto itself within the DAC. Of course, one of this franchise's strong suits (and a reason for its success) is its unique and unconventional characters, many of whom became Ensemble Dark Horses in their own rights.
Lilo & Stitch: The Series pilot Stitch! The Movie, the experiments as a whole became such Ensemble Dark Horses that they became the biggest defiers of Disney's tradition of not acknowledging the sequel material of Walt Disney Animation Studios films in their works (more on that on some of the entries below). Part of it may have to come from their Ugly Cute designs or for being Disney's version of Pokémon in a way.
- Now within the Lilo & Stitch franchise, protagonist Stitch (X-626) himself does not qualify as one. But on a broader scale, he is one of Disney's most popular characters and receives lots of merchandise even to this day, especially on Disney's lapel trading pins, despite that he's no longer one of the A-list characters in Disney's current marketing. Being a funny, cute, fluffy, Crazy Awesome badass with good Character Development certainly helps.
- Angel (X-624), for being a Cute Monster Girl and Distaff Counterpart of Stitch (and also for being initially voiced by famed voice actress Tara Strong). She was initially supposed to be a One-Shot Character when she was introduced late into The Series's first season, but many fans could not help falling in love with her. She and her episode won a poll held by Disney Channel in Spring 2004 for the fans' top ten favorite experiments and episodes in The Series' first season. As a result, she managed to get a second major appearance in the penultimate episode "Snafu" where she gets rescued, get a small scene in Series Finale Leroy & Stitch where she kicks Leroy clone patooki to protect Stitch, and finally fully break out as a major recurring character in the Stitch! anime. She is so popular that she is also the only experiment other than Stitch to have merchandise currently (as of 2019) sold in America, complete with her own shopDisney page, which is unheard of for a character from a long-since-ended Sequel Series. She even received some merchandise themed after Walt Disney World (including one of its parks) and Disneyland for some years before finally starting to make costumed appearances at Walt Disney World in the late 2010s. This is all despite that the Lilo & Stitch franchise has been practically dormant in North America since the end of The Series over a decade ago, and that the majority of her appearances in the franchise are still from the aforementioned anime that American fans tend to reject.note
- Reuben (X-625), for his laid-back, snarky personality; being voiced by Rob Paulsen certainly helps. Still, despite his status as a major character—having appeared in more episodes in The Series and the Stitch! anime than any other experiment besides Stitch himself—he gets overshadowed by his immediate successor and predecessor.
- Sparky (X-221), likely because of his role in Stitch! The Movie, his powers, and for being Ugly Cute. He was even popular enough to be a mandatory Boss Battle in Kingdom Hearts: Birth by Sleep, making him the first Disney Television Animation character to appear in the Kingdom Hearts franchise. He also received several recurring appearances in the anime and is even the only "cousin" to appear on this mural in Hanapepe◊—the town that inspired Lilo & Stitch's Kokaua Town.note
- Experiment 627, or "Evile" as the fans call him, due to the appealing concept of a tough experiment who's better than Stitch, and who would have likely become a rival to him had he received more appearances. He was number five on the aforementioned top ten poll.
- Bonnie (X-149) and Clyde (X-150), due to their personalities and Outlaw Couple dynamic, although Bonnie is the more popular of the two with her more appealing design, Tomboyish personality, and the fact that she's the only other prominent female experiment besides Angel whose body bores similarities to Stitch's.
- Leroy, despite being a Flat Doppelgänger of Stitch who only appeared in one television film, is also a popular experiment nonetheless, and has even received some merchandise including a Tsum Tsum plush. In fact, fans were delighted to see him again as a recurring boss and the final experiment to capture during a Lilo & Stitch: The Series-themed event in Disney Tsum Tsum held in September 2018 in Japan and January 2019 globally.
- Splodyhead (X-619) seems to also be one, considering his fight against Slushy (X-523) in that experiment's episode (and the extensive reuse of scenes from that fight in "Ace") and his cameo in Big Hero 6, which made him the very first character from a sequel series to a DAC film to appear in a later DAC film.
- Felix (X-010) is one due to his cute looks and hilarious obsession with cleaning as "Felix" or spreading dirt as "Oscar". Even the way he says "Dirty!" is oddly adorable. Japan especially loves him (and also a number of other experiments); not only does he make a few more appearances in the anime, he's even the only playable character outside of the mid six-twos in the Nintendo DS game Disney Stitch Jam.
- Slushy (X-523) due to the surprisingly wide range of abilities he shows from his ice-generating powers (as seen in his aforementioned fight with Splodyhead) and for his playful trickster personality. (In fact, he actually has one of the more fleshed-out personalities among the experiments.)
- Yin (X-501) and Yang (X-502) for their Opposites Attract dynamic. In fact, these two were seventh on that top ten poll.
- Sample (X-258) is a peculiar one for his upbeat, carefree attitude and ability to provide some fresh beats with the sounds he records.
- Of all the experiments that were introduced in Leroy & Stitch, Carmen (X-123) got the most attention due to her fun Carmen Miranda-inspired design and visual similarities to Angel. We didn't get to see what her ability was in the film, but thankfully, she eventually appeared in an episode of Stitch! ~Best Friends Forever~ and was given an ability that fits her very well.
- Bragg/Flute (X-145) or Twang (X-023) — a.k.a. that yellow cat/rabbit-like flute-playing experimentnote — only appeared in one episode of the Stitch! anime, but he's by far the most popular experiment who was introduced in (and remains exclusive to) that show. The anime's fans were won over by his wickedly deceptive personality underneath his charming exterior.
- Some of the experiments mentioned above (i.e. Angel, Reuben, Sparky, 627, Felix, and Sample) have also appeared as costumed characters in Tokyo Disneyland and Disneyland Paris alongside the main duo, and most of them have even begun making small appearances in Walt Disney World. All those same experiments appeared in "Stitch Meets High School Musical", a 2007 anime short parodying High School Musical. Also, in May 2019, Reuben, Sparky, Felix, and Sample finally got made into Tsum Tsum plushesnote and were released as part of a special "Stitch and Friends" set in Japan.
- Ice Cream Man. So much that he was the only Lilo & Stitch character other than Lilo, Stitch and Nani to be made into a Townsperson costume in Disney Infinity, where he costs 100,000 blue sparks in 2.0's Toy Store.
- Lilo's doll Scrump is not even alive (save for that one time Phantasmo possessed "her") and only plays a small role to Lilo's character, but "she" gets a lot of fan art and merchandise (albeit, oddly appearing with Stitch more than with Lilo instead), which even includes a couple Funko Pop! vinyl figures modeled after "her". The best evidence supporting this has to be in this official fan art contest held by Disney and BoxLunch (Hot Topic), where Scrump appeared on eight of the twenty-five chosen finalists for the contest (tied with Lilo as the second-most appearing character), six of which feature only "her" and Stitch together.note
- Amy Hill as Mrs. Hasagawa is a very memorable character even if she appears only once in the original film. Thankfully, The Series gave her a few more appearances, including involving her in a B-Plot of the American Dragon crossover episode and even making her the focus of half of a Two Shorts episode.
- The blonde lifeguard whom Nani briefly talks with for a job is extremely popular, for some strange reason.