Since most Rick and Morty side characters that aren't from Morty's school rarely, if ever, show up again after their first appearance, this happens a lot due to their memorable designs and/or personalities.
Alternate Versions of the Titular Duo
- The nature of the show means that we spend time with many variants of Rick and Morty, and many of them are effective as their own characters
- One specific example from episode "Close Rick-Counters Of The Rick Kind" is Evil Morty, who's only appeared four times so far, but is wildly popular for his memorable reveals, complete with Awesome Music for both (to the point that For the Damaged Coda is now considered to be his Leitmotif), and managing to successfully escape and outsmart the main and alternate versions of Rick in his first appearance, and become president of the Citadel of Ricks without any still-living Citadel member figuring out who he really is or what he really wants in his second appearance. Fans rejoiced when he made his appearance in "Rickmurai Jack" and finally became a direct threat to Rick and Morty, being revealed to have created thousands of Morty clones and using them to destroy the Central Finite Curve, the Citadel, and Rick and Morty so he can escape into realities where Rick is not the smartest man in the universe. Evil Morty is the definition of The Chessmaster. And then came "Unmortricken", in which he returns yet again and helps Rick get his revenge on Rick Prime for killing his family, getting the schematics of the Weapon Too Cool for a Name out of it.
- From the same episode, we got Doofus Rick, for being a lovable Nice Guy who bonds with Jerry of all people and compared to the other Ricks in this show, that alone is something pretty special.
- Hammerhead Morty, who is merely a one-off joke, but many were still concerned when he was shot multiple times in the Season 3 premiere. He's quite popular among Pocket Mortys players, due to being one of the few collectible Mortys who actually appeared in the show.
- "Baseball Cap Morty" and "Girl Morty", who appeared very briefly in the background in the Season 3 premiere "The Rickshank Redemption", are very popular, due to being a Shout-Out to another show that's Friendly Fandoms with Rick and Morty.
- The Rick/Morty-fusion seen alongside the Morty twins in the background is also quite popular, mainly due to Fusions in general being a popular concept among fandoms, as well as fans liking to speculate what he would act like or how he came to be.
- Pickle Rick isn't from an alternate dimension but became one heck of a Memetic Mutation long before his titular episode aired.
- "Simple Rick", due to being arguably the most tragic Rick among the Ricks introduced in "The Ricklantis Mix-up".
- Morticia, from the Pocket Mortys game is the first female Morty and that alone has generated a lot of love for her.
- Wasp Rick from "Edge of Tomorty: Rick Die Rickpeat" became an instant hit due to being one of the nicest and most helpful versions of Rick despite his menacing appearance, and for the hilarious juxtaposition of him and his family having a polite, happy conversation while horrifically eating his universe's Mr. Goldenfold alive.
- Twenty-six year old Morty from "Rickmurai Jack" is rather well liked, despite only having a few seconds of screen time. He acts heroic in his brief time and is widely considered handsome. He eventually reappears (in a way) in "Fear No Mort", during an apparent Time-Passes Montage where Morty grows up and goes into college.
- One specific example from episode "Close Rick-Counters Of The Rick Kind" is Evil Morty, who's only appeared four times so far, but is wildly popular for his memorable reveals, complete with Awesome Music for both (to the point that For the Damaged Coda is now considered to be his Leitmotif), and managing to successfully escape and outsmart the main and alternate versions of Rick in his first appearance, and become president of the Citadel of Ricks without any still-living Citadel member figuring out who he really is or what he really wants in his second appearance. Fans rejoiced when he made his appearance in "Rickmurai Jack" and finally became a direct threat to Rick and Morty, being revealed to have created thousands of Morty clones and using them to destroy the Central Finite Curve, the Citadel, and Rick and Morty so he can escape into realities where Rick is not the smartest man in the universe. Evil Morty is the definition of The Chessmaster. And then came "Unmortricken", in which he returns yet again and helps Rick get his revenge on Rick Prime for killing his family, getting the schematics of the Weapon Too Cool for a Name out of it.
Recurring Characters
- Mr. Poopybutthole from the episode "Total Rickall" has a lot of fans. His reappearance at the end of the season 2 finale was very well-received, and he was promoted afterwards to a recurring character.
- Morty's teacher Mr. Goldenfold has his fans, if mainly due to his hilarious lines and odd personality. He eventually gets his Day in the Limelight in Season 7's "Rise of the Numbericons: The Movie".
- Morty's crush, Jessica is considered to be an interesting character in her own right, going off her casually amiable relationship with Morty, very quick adjustment to the weirdness surrounding the Smith family, and her lack of familial relationship to Rick, all of which could give her a unique perspective on their absurd adventures.
- Tricia Lange is popular amongst the fanbase for her attractive design. She features in quite a lot of fanart, and it’s likely that the writers have noticed her popularity as she's gone from making a brief appearance in her debut to one of the show's most recurring background characters to being one of Summer's friends.
- Diane Sanchez, Rick's wife from "Rickshank Rickdemption" is immensely popular among fans, despite never appearing in person in the present. Mostly because she was a supportive wife and had a very Tear Jerker death scene that was the Start of Darkness for our Rick's nihlism. We even get to hear her voice for the first time as a digital ghost in season 6.
- Dr. Wong, the psychiatrist from "Pickle Rick", has gained a decent fanbase for her calm, composed manner as she analyzes the family and how she responds to Rick belittling her profession by deconstructing how Rick behaves: he uses intelligence to justify his misery and goes on adventures to escape the mundane if often more practical, just to prove to himself that he alone dictates his destiny.
One Shot Characters
- Mr. Meeseeks who first appeared in "Meeseeks And Destroy" seldom appears, but he's one of the most popular characters in the show.
- Krombopulous Micheal, the insectoid assassin that only appeared in "Mortynight Run", is incredibly popular for being so upbeat about his job and doing it with such style.
- Scropon from episode "Ricksy Business" has some fans as well due to his monstrous but very cool looking alien appearance and tragic backstory about his planet being destroyed. He was loved by some of the writers who drew early concepts on him with one such writer making a note saying that Scropon looked cool on one of the earlier concepts.
- Scary Terry from episode "Lawnmower Dog" is pretty well-liked due to being a parody of Freddy Krueger, a horribly bad Pungeon Master, and a surprisingly Nice Guy who's actually just a Punch-Clock Villain.
- Noob Noob from episode "Vindicators 3: The Return of World Ender", the Mr. Poopy Butthole look-alike who can't seem to catch a break.
- Crocubot is probably the most popular of the group for being the least immoral and most willing to own up to the mistakes of the group. His cool design also helps too. His death was met with some legitimate mourning.
- Tony from the Season 4 episode "The Old Man and the Seat", is quite popular despite his single appearance, with many people admitting to liking his somewhat friendly and likeable but still subtle personality. His death makes this even sweeter, as the scene of Rick grieving Tony on his private toilet surrounded with various holo-recordings of himself is generally agreed to be an incredible Tear Jerker.
- The Talking Cat in "Claw and Hoarder: Special Ricktim's Morty" for his mysterious nature. Many fans agree that his subplot with Jerry is better than the A-Plot of the episode.
- The Tuskfish Aliens (who are the pink-skinned muscular blue-eyed aliens serving as background characters). For anyone who views an entire species of aliens on the show as extremely popular, these guys qualify. They got quite a bit of fanart devoted to them and are popular for the amount of Mr. Fanservice they provide. Among them, the Hookah alien is quite popular.
- Morty's Girlfriend only appears for less than ten minutes in "The Vat of Acid Episode", but thanks to the relationship she and Morty build—with no dialogue—throughout the episode, fans are really hoping she'll make more appearances in the future.
- The gangsters also in "The Vat of Acid Episode", if for no other reason than their reaction to the apparent suicide provides some of the most hilarious portions of what is widely considered one of the best episodes of the series.
- Rick's arch-nemesis Mr. Nimbus, who only appeared in episode "Mort Dinner Rick Andre", has a lot of fans for being a hilarious Large Ham and a great Foil to Rick.
- Similar to Morty's one-shot girlfriend from Season 4, Planetina from episode "A Rickconvenient Mort" instantly became a fan-favorite, with the added bonus of being her own character rather than a Satellite Love Interest.
- Of the five real GoTron pilots from episode "Gotron Jerrysis Rickvangelion", Kendra is the most popular thanks to being the most prominent among them and for actually being rather attractive between her design and Animesque style (she's more cute than sexy, but she still has her fans). Helps that she was the only one of the original pilots to be named.
- Hermit Jerry has gained some popularity with fans for his Took a Level in Badass compared to the Jerry that we are familiar with in his appearance in "Solaricks", but also for his "The Reason You Suck" Speech to Morty, spelling out how many of the sociopathic traits associated with Rick he sees in his son. Whereas regular Jerry begs his children for validation, Hermit Jerry is repulsed by Morty's claim that he "improved" during the Cronenberg apocalypse. His expression of hurt and rage to Morty is perhaps among Chris Parnell's best voice work for the show, and made Rick Prime that much more of a Hate Sink for killing Hermit Jerry in The Stinger.
- The Fear Hole from "Fear No Mort" is among the most beloved villains of the series for being a genuinely scary Knight of Cerebus and for its darkly charismatic, Affably Evil personality.
