Rick and Morty is a really unique show that manages to blend complex sci-fi concepts it manages to balance while also being incredibly funny which is due in large part to the zany characters in the series and the actors that voice them. In addition to being one of the co-creators of the show along with Dan Harmon, Justin Roiland also provides the voices for a lot of the characters on the show.
While the characters he voices can vary from minor appearances to major roles, some have fan favorites over time and become iconic from the moment they first appeared onscreen.
The Truth Tortoise
The Truth Tortoise appears briefly at the start of "Morty's Mind Blowers". Morty is holding the creature while he and Rick are running from Morpheus when Rick instructs him not to look into the tortoise's eyes, warning him that if he does he'll know everything despite the fact that Morty had been doing exactly that the entire time.
The tortoise then says "Daed si luap, eltaeb a mi" before Morty drops it. The phrase backward is "I'm a Beatle, Paul is dead" which is a reference to a conspiracy theory that alleges that Paul McCartney had died in 1966 and was replaced by a duplicate. This then leads into the events of the episode with Rick offering to wipe Morty's mind and it being revealed that he had already done so hundreds of times.
Taddy Mason
Taddy Mason is a man who runs a hotline that lonely adults can call and talk about anything, a service that Jerry, who was unemployed, took full advantage of. In the episode, "Look Who's Purging Now", Jerry frequently asks Summer if that who's on the phone when Rick calls her for help.
In the post-credit scene, Beth comes into the living room to question Jerry as to why their phone bill is so high and why so many calls were made to someone named Taddy Mason. As she does, a commercial for the service appears on television as Jerry frantically tries to turn the television off and has to result to unplugging it all together before she coldly tells him he needs to get a job.
Ants in my Eyes Johnson
In the episode, "Rixty Minutes", Rick introduces Morty and the rest of his family to the International cable box which allows them to watch shows and ads from other dimensions.
One of the commercials features a character named Ants in my Eyes Johnson who is the owner of a store that sells various electronics but suffers from a condition that doesn't allow him to feel anything or see anything resulting in a bunch of ants crawling around his eyeballs. The fact that the majority of these segments are improvized only adds to the hilarity.
Eyehole Man
Eyeholes man is another interdimensional character and was introduced in the sequel episode "Interdimensional Cable 2: Tempting Fate". Eyeholes man is an alien superhero mascot for the "Eyeholes" cereal who runs around with a megaphone and beats up anyone who actually tries to eat the cereal, claiming that he is the only one that can have it.
While the commercial is hilarious, the funniest moment comes during the episode's post-credits scene where he comes in and attacks Jerry after he tries one of the Eyeholes and has to be rescued by Rick, Summer, and Morty.
Noob-Noob
Noob-Noob was the often ignored intern for the superhero group, The Vindicators. He was introduced in "Vindicators 3: The Return of Worldender" which saw Rick and Morty team up with the superhero group for the second time after an off-screen crossover.
Noob-Noob has a clear desire to join the main team but is forced to stay behind from the mission to clean after Rick gets drunk and destroys the team's base. Fans would learn later in the episode that the mission was set up for Noob-Noob by drunk Rick to thank him for laughing at his jokes, saying that he was the only one who got him.
The Cromulons
The Cromulons are a species of giant head-shaped beings from the Cygnus-5 expanse that come in an assortment of different colors. They first appeared in the episode,"Get Schwifty", when they forced Earth and several other planets to participate in a reality tv competition called Planet Music which they also host.
Many who saw them, believed them to be Gods and began worshipping them. They were ultimately defeated and left Earth when Rick and Morty performed the song the episode was named after and spared the planet in the process.
Mr. Poopybutthole
Mr. Poopybutthole is first noticed in the episode "Total Rickall" where he's revealed to be a long-time friend of the family that the audience just happens to not remember. The episode follows the Smith family as they deal with a parasite that invades minds and implants false memories.
He ends up getting shot at the end of the episode by Beth after she realizes that she doesn't have any negative memories of him which was the method they used to identify the parasite. He would go on to be a recurring character on the show, often appearing in various post-credit scenes while on his path to recovery.
Mr. Meeseeks
Mr. Meeseeks are blue creatures that appear when a Meeseeks Box is activated. It is the job of a Mr. Meeseeks to help whoever pressed the button to achieve any task they want to accomplish.
The character was first introduced in the episode "Meeseeks and Destroy" when Rick gave one to his family to share, leading to chaos when Jerry asked for help with golf. Seeing the creatures go insane and become homicidal while struggling to help Jerry with what should have been a simple task makes them one of the more interesting minor characters from the series.
Morty Smith
Morty Smith is Rick's 14-year-old grandson and the second main protagonist of the series. While he can sometimes seem naive, he is much smarter and much more capable than people, especially Rick, give him credit for.
Like with Rick, Roiland voices the alternate versions of the character from the multiverse, which includes Evil Morty who has been silently operating in the background towards an unknown goal.
Rick Sanchez
The most popular character Roiland voices Rick Sanchez, one of the show's title characters and is the alcoholic yet genius inventor of most of the devices that get those around him either in or out of stressful and dangerous situations.
While he often presents himself as arrogant and unaffectionate, it's clear that he does care about his family. In addition to the main C-137 version of Rick, Roiland also voices the alternate versions of him including Doofus Rick, Simple Rick, and Wasp Rick.