In the titular episode, he holds Candy People hostage. His intentions were to steal Princess Bubblegum's crown due to an event in his past. In his youth, Princess Bubblegum visited an orphanage he lived in to cheer all of the depressed children up. When Baby Snaps told her he wanted to be a princess like her (so he could also make children happy, like she did for them), Bubblegum giggled a bit and patted his head. Cookie saw this gesture as an act of scorn.
Cookie befriends Jake (who is disguised as a milk man) thinking that he also hates Princess Bubblegum. When Jake hears his story he suggests that he should start over and rule over a new place, where people can follow their dreams. To this Cookie agrees, and the two try to escape, but are pursued by the Banana Guards.
Cookie eventually becomes disheartened and agrees that he'll never be a princess. To avoid being sent to jail by the Banana Guards, he attempts to fall off a cliff into the Candy Gorge; however, he survives, although broken in many pieces.
At the end of the episode, he is re-assembled in the Candy Kingdom Mental Hospital. He is playing chess with a Candy Person when Jake gives him the crown from the Grass Lands making him its unofficial princess.
He appears to be still in the Candy Kingdom Hospital by the episode "Jake the Brick". He seems to have recovered from the fall, but without his chips.
He is able to deploy his chocolate chips as allies. He communicates with them via walkie-talkie. Their names are Chipler, Chipolina, Chipper, Chipton, and Chipface.
- Princess Cookie knows how to play chess. He also knows algebraic chess notation, since he tells one of his chips where to move his pieces.
- Princess Cookie takes the title of "Princess," despite the fact he is still a male. The appropriate equivalent is "Prince" - possibly the reason why he wanted to become a "Princess" is because the only ruler he knew at the time was Princess Bubblegum.
- According to CN Latin America, he sends a "Hello" to all his crumbs and chips, and he does not have a wish since it was fulfilled: he's a princess.