The 9 Best Guest Stars on 'Rick and Morty,' Ranked

In the ever-complicated universe of Rick and Morty, all manner of aliens and interdimensional beings trickle in and out of Rick and Morty’s orbit. There are creatures from Pluto, bug-like members of the Galactic Federation, beings from the fourth dimension, and even interdimensional puffs of gas.

One of the show’s creators, Justin Roiland, voices both Rick and Morty, and he’s joined by a solid core cast that includes Sarah Chalke (Scrubs) as Beth, Chris Parnell (SNL) as Jerry, and Spencer Grammer (Greek) as Summer. In addition to them, though, Rick and Morty has made good use of many big names in comedy and beyond to voice characters on the show. Names both big and small from the worlds of animation and comedy have graced Rick and Morty, and even though each has made a great show even better, a number of them have really stood out as memorable.

Here are the nine best guest actor voice roles that have been included on Rick and Morty:

9. Andy Daly as Krombopulos Michael

Actor Andy Daly has a wide-ranging comedic background on television, but is perhaps best known for starring as Forrest MacNeil on the Comedy Central series Review.

He brings an undeniable charm to fan favorite character Krombopulos Michael, the ever-pleasant Gromflomite assassin who Morty accidentally killed in “Mortynight Run.” He’s oppressively positive and jolly despite killing people for a living, and he delights in delivering death, despite age or gender. He “just loves killin’!

Krombopulos Michael is easily one of the best minor characters from the show ever and some fans used to think he’d play a role in breaking Rick out of jail in Season 3, which turned out not to be the case. Regardless, we’d all love to see the happy-go-lucky assassin make a return to the show.

8. Keegan-Michael Key as 5th Dimension Testicle Monster #1

Keegan-Michael Key is the Key half of the Key & Peele comedic duo, and he brings his energy and intensity to his role as a “5th Dimension Testicle Monster” in Rick and Morty.

In a truly zany Season 2 premiere, Rick unfreezes time after six months spent repairing the house after a disastrous but fun party. Summer and Morty’s uncertainty causes time itself to splinter into an array of fragments. When trying to re-merge the timelines, Rick causes another time fracture that attracts the attention of the bizarre 5th Dimension Testicle Monster. As it turns out, Rick stole a Time Crystal from the Testicle Monsters, and this particular Monster is really mad about it and threatens Rick, Morty, and Summer by shouting profusely and wielding a living Slug Gun.

7. Matt Walsh as Sleepy Gary

Matt Walsh is perhaps most often recognized from his role as Mike McLintock in HBO’s Veep, the bumbling former White House Press Secretary and Director of Communications.

On Rick and Morty, Walsh plays the overwhelmingly earnest Sleepy Gary, who’s actually an alien parasite looking to take over Earth. In one of Rick and Morty’s all-time best episodes, “Total Rickall,” his species of replicating parasites create fake beings by implanting positive, false memories in hosts. Despite an odd name and choice of clothing (always pajamas), Sleepy Gary is otherwise a really nice guy. In the fake memories featuring Sleepy Gary, it’s him that’s married to Beth and father to Morty and Summer — Jerry is just sort of uselessly along for the ride, which feels pretty believable. In fact, Sleepy Gary is the only one that seems to love and cherish Jerry, as made evident by a memory of Gary and Jerry being secret lovers.

6. David Cross as Prince Nebulon

Best-known as oddball Tobias Fünke on Arrested Development, David Cross is the petulant Prince Nebulon, leader of the Zigerions, in Rick and Morty’s fourth episode ever: “M. Night Shaym-Aliens!”

Nebulon has a grudge against Rick and tries to steal his recipe for Dark Matter by placing him inside a simulation … inside a simulation. He’s a bit of a bumbling and ineffectual arrogant fool that Rick delights in outsmarting. Nebulon also has a peculiar aversion to nudity. It’s almost unfortunate that Rick blows up the Zigerion ship by the end, killing Nebulon in the process.

5. Nathan Fillion as Cornvelious Daniel

Nathan Fillion might be one of the highest-profile guest stars to grace Rick and Morty, and he did so in the Season 3 premiere. Fillion is widely loved for his role as the lead in Joss Whedon’s gone-too-soon Firefly. He was also a lead in Castle, which saw a 173-episode run. Gamers might also recognize him as the voice of Cayde-6, an android central to the plot of the Destiny video game franchise.

In “The Rickshank Redemption,” Fillion lends his voice to Cornvelious Daniel, the Gromflomite Galactic Federation Agent that invades Rick’s mind to get the formula for inter-dimensional travel via a brain-link. He’s a no-nonsense smooth talker that reveals how Gromflomites experience arousal, which is when their “flappy doodles twitch.” Daniel is also fortunate enough to sample the Mulan Szechuan Sauce within Rick’s memories.

4. John Oliver as Dr. Xenon Bloom

John Oliver’s career really blossomed thanks to his widely beloved Last Week Tonight news recap and analysis show on HBO, but his boisterous British enthusiasm has lent itself to a solid comedic career with programs like The Daily Show with Jon Stewart, Community, and a diverse array of voices on animated programs.

In Rick and Morty’s third episode, “Anatomy Park,” Oliver voices Dr. Xenon Bloom, Rick’s partner on a venture to establish a biological amusement park inside the body of a human being. Bloom is a sentient amoeba meant to satirize John Hammond, the creator and CEO of the original Jurassic Park. As such, his goofy character has spectacles and a mustache and walks with a cane. He’s goofy and bizarre and like many guest characters, meets a blunt and unfortunate end that’s so very easy to laugh at when he stays behind to activate the Bone Train and gets killed by E. coli before realizing that he could have just used auto-pilot.

3. Stephen Colbert as Zeep Xanflorp

Stephen Colbert is most prominently known for taking over The Late Show after David Letterman retired in 2015, following up previous success with The Colbert Report.

Zeep Xanflorp is a brilliant but arrogant scientist living in the Microverse Battery that powers Rick’s car. Xanflop creates his own micro-planet power supply called the Miniverse in a similar fashion to Rick’s own battery, which causes power supply problems with Rick’s vehicle. Xanflorps difficult personality and utter contempt for everyone else perfectly mirrors Rick’s, as does his almost random addiction to opium.

2. Jemaine Clement as Fart

His velvety voice is most often heard as one-half of the comedic musical duo Flight of the Conchords with Bret McKenzie, but Jemaine Clement has built up and acting and voice work for animated shows and features in recent years in films like Moana and The Lego Batman Movie.

Clement voices “Fart” in Rick and Morty’s “Mortnight Run” episode. Though technically an unnamed interdimensional gaseous being, the powerful cloud assumes the name Fart after Rick insults it. Fart is the being that assassin Krombopulos Michael was hired to kill, but Morty takes efforts to prevent that. Ultimately, Fart reveals his intention to wipe out all carbon-based life and Morty kills him anyway. Clement’s deadpan delivery of cosmic wisdom and trippy impromptu musical numbers offer up something refreshing and new to Rick and Morty.

1. Werner Herzog as Shrimply Pibbles

The ever-intimidating Werner Herzog is something of an enigma in the list of Rick and Morty guest stars. The intimidating German screenwriter, director, and actor has had a long career that includes narrating many of his own high-quality documentaries with his signature thick accent. In the same year he appeared on Rick and Morty, he also had a hilariously serious role on Parks and Recreation.

In Rick and Morty, Herzog plays alien civil rights leader Shrimply Pibbles, who is basically intergalactic space Gandhi. The heart of the revered leader is failing, and doctors in a hospital discover that if Jerry Smith donates his penis, they can convert it into a functioning heart for the leader. Aside from Jerry and Beth’s problematic, but funny, reactions to the predicament, a standout moment from the episode is Shrimply Pibbles’s monologue about human society: “Their entire culture is built around their penises.” There’s nothing like hearing low-brow humor being delivered by the same voice that narrated Grizzly Man.