She was first introduced in the Adventure Time episode "Fionna and Cake" as a genderbent version of the show's lead character Finn the Human.

Fionna Campbell and Cake the Cat were created by Adventure Time storyboard artist Natasha Allegri as fan art.

[2] In an interview with Comic Book Resources, Allegri stated that she first designed the characters after someone on an online forum requested that she draw genderbent fan art.

[3] Allegri shared her drawings of the characters on Tumblr, where they become popular with fans,[1] later sending them to Frederator Studios, one of the production companies behind Adventure Time.

[1] In August 2021, it was announced that HBO Max had greenlit a young adult animated series focusing on the characters of Fionna and Cake.

[2] Together with her cat Cake, Fionna emerges from the head of their creator Simon Petrikov, the former Ice King, and find themselves inside of the magical universe of Ooo.

[16] Sava gave the episode a positive review, praising the portrayal of Fionna and Martin's vocal performance, which he described as having "a youthful energy but also a pubescent scratchiness".

[8][9][12][10] Gary Catig of AIPT wrote that the character's narrative arc focused on struggles common to young adults including self-discovery and a desire for independence.

[8] In a review for Den of Geek, Rendy Jones also praised the character's relatable struggles, writing that she and Cake "evolve beyond their once stunt-marketed gender-flipped archetypes and grow as their own unique beings.