Honestly, the transition from Adventure Time to the spin-off series Fionna and Cake wasn't just about swapping genders or making things "edgy" for an older audience. It was a massive gamble on voice acting. When you look at the Fionna and Cake cast, you aren't just seeing a list of names; you’re seeing a masterclass in how to evolve characters that fans have literally grown up with over a decade. It’s weird. It’s messy. It’s surprisingly emotional.
The show takes these "fan-fiction" characters—originally created by the Ice King as a weird self-insert hobby—and forces them into a cold, magic-less reality. That shift required the actors to do something most voice performers never have to: play the "normal" version of a cartoon icon.
Madeleine Martin: Making Fionna More Than a Finn Clone
Madeleine Martin had a tough job. She’s been the voice of Fionna since the character first appeared in Season 3 of the original series back in 2011. Back then, Fionna was basically just "Girl Finn." She was adventurous, she punched stuff, and she had that high-energy heroic vibe.
But in the new series? Fionna is a broke, depressed young woman living in a studio apartment with a cat that won't stop puking.
Martin’s performance changed. You can hear it in the rasp. She moved away from the "mathematical!" enthusiasm of her teens and leaned into a grounded, slightly exhausted tone. It’s what makes the show work. If Fionna sounded like a Saturday morning cartoon character while trying to pay rent in a gray city, the show would’ve flopped. Martin brings a specific kind of millennial burnout to the role that feels painfully real.
She isn't just "Finn with a ponytail." She's a person looking for magic in a world that feels like a dead end.
The Chaos of Roz Ryan as Cake the Cat
If Madeleine Martin is the anchor, Roz Ryan is the rocket fuel. Cake is arguably the loudest, most vibrant part of the Fionna and Cake cast, and that is 100% due to Ryan’s legendary vocal range.
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Most people know Roz Ryan from her extensive Broadway background or her role as Thalia, the Muse of Comedy in Disney’s Hercules. That theatricality is everywhere in Cake. But here’s the nuance: in the spin-off, Cake is the one who starts "glitching" back into her magical self first. Ryan has to balance two versions of the character. One is a regular, meowing housecat. The other is a giant, stretching, sassy magical entity.
The way Ryan switches from a guttural growl to a soulful, belting laugh is something you don't see often in modern animation. It’s old-school. It’s loud. It’s exactly what a chaotic cat should be.
The Return of the King (Sort Of)
Tom Kenny is a legend. We know this. He’s SpongeBob, he’s the Ice King, he’s basically half of your childhood. But his role in the Fionna and Cake cast is actually heartbreaking. He’s playing Simon Petrikov—the man who used to be the Ice King.
Simon is a man out of time. He’s a 20th-century scholar living in a 1,000-year-later candy-coated apocalypse. Kenny plays him with this incredible, fragile dignity. He doesn't use the high-pitched, screechy voice of the Ice King anymore. Instead, he uses a softer, more rhythmic speaking style that makes you realize just how tired Simon is of being alive.
It’s a performance about trauma.
When Simon tries to "re-enact" being the Ice King for fans in Ooo, Kenny’s voice cracks in a way that’s genuinely hard to watch. It’s a meta-commentary on the actor himself, playing a character who is tired of playing a character.
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Andrew Rannells and the New Blood
The show didn't just stick to the O.G. crew. It brought in some heavy hitters to flesh out the multiverse. Gary Prince—the "normal world" version of Prince Gumball—is voiced by Andrew Rannells.
If you like musical theater or Girls, you know Rannells. He brings this polished, slightly pretentious but ultimately sweet energy to Gary. The chemistry between his Gary and Marshall Lee (voiced by Donald Glover) is a huge draw for the "Bubbline" fans who wanted to see the male-coded version of that romance.
Wait, let's talk about Donald Glover for a second.
Getting Glover back for Marshall Lee was a huge win. He’s busy. He’s Childish Gambino. He’s doing Atlanta. But his presence in the Fionna and Cake cast gives Marshall Lee that effortless, cool-guy-with-daddy-issues vibe that no one else can replicate. His singing voice? Smooth. His attitude? Detached. It’s the perfect foil to the high-strung energy of the rest of the group.
Why the Supporting Cast Matters
The multiverse hopping allows the show to bring back iconic voices in terrifying new ways.
- Hynden Walch: She’s usually the bubbly Princess Bubblegum, but in this series, she voices "The Star," a version of PB that is a literal vampire hunter/dictator. It’s chilling.
- Jeremy Shada: Yes, Finn is back. But he’s "Farmworld Finn" and "Big Destiny Finn." Shada has to play Finn as an adult, which is a trip for anyone who remembers him as a 12-year-old kid in 2010.
- Felicia Day: She joins as Betty/Golb-related entities. Her voice has this ethereal, frantic quality that perfectly matches the cosmic horror elements of the show.
The genius of the Fionna and Cake cast isn't just the names on the list. It’s the history. Every time you hear a voice, you’re hearing ten years of character development. You’re hearing the actors age alongside the audience.
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The Weird Multiverse Cameos
One of the best parts of the show is spotting the "alt" versions of minor characters. You’ve got characters like Choose Goose (Jeff Bennett) showing up in ways that are deeply depressing or surprisingly heroic.
The casting directors, Jenny McKee and Sara Jane Sherman, clearly understood that this show wasn't just a spin-off; it was a goodbye to the world of Ooo. They brought back the people who mattered. Even when a character only has three lines, like Prismo (voiced by the incredible Kumail Nanjiani), those lines carry the weight of the entire franchise's mythology. Nanjiani’s deadpan delivery as a wish-granting deity who is basically a bored IT guy is still one of the highlights of the entire series.
Directing the Madness
Adam Muto, the showrunner, has mentioned in various interviews that the recording sessions for this show were different. Because the themes are more adult—dealing with depression, legacy, and the fear of irrelevance—the direction was more "cinematic."
They weren't just looking for funny voices. They were looking for breath. Pauses. The sounds of someone actually thinking. That’s why the Fionna and Cake cast sounds so "human" compared to the more hyperbolic style of the early Adventure Time seasons.
Key Takeaways for the Ultimate Fan
If you’re looking to dive deeper into the world behind the microphone, here is what you need to pay attention to on your next rewatch:
- Listen to the Pitch: Notice how Madeleine Martin drops her voice an octave when Fionna is in her "normal" world versus when she's in Ooo. It’s a subtle cue of her comfort level.
- The Simon/Ice King Contrast: Tom Kenny does a "breathy" version of Simon that is distinct from his "nasal" Ice King. It’s a physical feat of vocal cord control.
- The Guest Stars: Keep an ear out for Vico Ortiz and other guest performers who bring a modern, diverse energy to the multiverse.
The Fionna and Cake cast proves that voice acting is more than just talking into a mic. It’s about carrying the soul of a character across different realities and different stages of life. Whether it’s the heart-wrenching nostalgia of Tom Kenny or the gritty realism of Madeleine Martin, these actors turned a "gender-swapped" gimmick into one of the most poignant animated shows of the decade.
Go back and watch the "Cheers" sequence in the later episodes. If you don't get chills hearing those specific voices harmonize, you might need to check your pulse.
To really appreciate the work here, look up the behind-the-scenes recording clips often shared by the crew on social media. Seeing Roz Ryan's facial expressions while she records Cake explains everything you need to know about why that character feels so alive. Pay attention to the credits—sometimes the "additional voices" are former writers and storyboard artists, keeping the show's DNA strictly "in the family."