True to his name, Jiminy is an anthropomorphized cricket, though he bears virtually no resemblance to real-life crickets. He has olive skin, thin black eyebrows, four-fingered hands, and wears the famous white gloves many older Disney characters wear.
He dresses very formally, wearing a royal blue top hat with an orange band near the base, a red vest with a single, pink button on the front, a yellow ascot, a black blazer, and a high-collared white shirt. He also sports tan pants and yellow shoes with black tips. Jiminy also carries a red umbrella.
Jiminy first makes his appearance in Disney Castle and becomes Sora, Donald, and Goofy's royal chronicler under the order of Queen Minnie. He explains to Goofy that he escaped right before his world was destroyed, and he was scattered from his friends. After they befriend Sora, they travel to many different worlds in search for the King, Riku, and Kairi. Some time after, he meets up with Pinocchio in Traverse Town, and tells him to stay put while he sets out to find Geppetto, his father.
When they head for Atlantica or Halloween Town, depending on which world the player chooses, they get swallowed by the giant whale Monstro and meet up with Pinocchio again, this time reunited with his father Geppetto. But then Pinocchio was lured away from his friends by Riku and they searched for him until a Parasite Cage Heartless captured Pinocchio and attempted to take his heart.
He failed, but then Riku captured him and stole his heart in hopes to be able to replace Kairi's heart. Jiminy, Sora, Donald, and Goofy manage to restore Pinocchio's heart with the united power of their hearts. Then, they battle Parasite Cage again and defeat it once and for all, but then Monstro feels ill and spit them out and separates Jiminy away from Pinocchio. He finds out that Pinocchio and Geppetto are okay after they visit Traverse Town again and find them living there.
Jiminy appears alongside Sora, Donald, and Goofy, and his role in this game is much more important; he appears more often, and during the game he is the one that tries to keep the team together. He is alone with Sora when Sora runs away from Donald and Goofy.
Like the others, his memories are also disappearing the more they head for each level of Castle Oblivion. Even the entries in his journal have disappeared altogether upon entering Castle Oblivion.
When Sora gets angry at Donald and Goofy for not wanting to help save Naminé, he sets out to find her by himself. Jiminy tries to reason with him, but he refuses to listen. When they finally meet Naminé, they find out from her that they have not actually met, but were rather fooled by her abilities to control memories of Sora and those attached to his heart. But Sora forgives her for her doing and they all set out to fight against those who made Naminé do what she did.
After the protagonists finally defeat Larxene, Vexen, and Marluxia, the members of Organization XIII, Naminé takes them to a room of Memory Pods, where she tells them she will be able to restore their memories while they sleep in them. But it will take some time, because reconnecting memories is harder than severing them.
However, as a price they will lose their memories of all things that happened while they were in Castle Oblivion. Afraid that they might not be able to thank her for what she does for them, Jiminy writes down a small entry in his journal that says "Thank Naminé".
In Kingdom Hearts II, Jiminy only appears once in the beginning of Sora's awakening.
A year after the events of Kingdom Hearts: Chain of Memories, Sora, Donald, Goofy, and Jiminy awake from their long, deep slumber in Twilight Town, and have no memories of what happened right after they closed Kingdom Hearts. Goofy asks Jiminy what his journal says, and Jiminy only finds a sentence: "Thank Naminé". Unable to know who she is anymore, Donald scoffs at him for his bad journal entry and Jiminy dismisses it by telling him to go and find out where they are. Jiminy doesn't reappear in the game after this event.
Jiminy reappears in Kingdom Hearts coded. His journal compiled in previous games is a major plot element, as well as a main character.
Jiminy is reorganizing his journal when he suddenly finds a sentence saying "We must return to free them from their torment". Jiminy cannot recall any memory of that entry, so he shows the text to King Mickey. To investigate, King Mickey creates a Sora out of data to try and find out more about the mysterious entries that continually appear.
As Sora continues to unravel the Bug Blox Corruption that is affecting the Datascape, Jiminy somehow gets sucked into the data world, along with King Mickey, Donald, Goofy and Pete. At the game's climax, however, he is presumably sent back to the real world along with his friends after the debugging of the journal is complete.
Jiminy Cricket appears in Kingdom Hearts 3D: Dream Drop Distance, as a resident of the sleeping world of Prankster's Paradise. He resides in Geppetto's home and was ordered by the Blue Fairy to educate Pinocchio. He will also encounter Riku. This Jiminy Cricket in Prankster's Paradise does not have the same memories of the Jiminy Cricket that was present with Sora and his companions in the previous adventures.
In Pinocchio, Jiminy serves as the main character's conscience. The Blue Fairy, who brought Pinocchio's puppet body to life, gave Jiminy the task of guiding him and helping him to determine right from wrong. However, Pinocchio's naivety, more than once, gets the better of him, leading to Jiminy losing his temper several times and scolding him. At one point, Jiminy prepares to abandon Pinocchio altogether, but rushes to the puppet's aid upon realizing he is in danger.
Eventually, their friendship prevails and Pinocchio, despite sacrificing his life to save his father from Monstro, is turned into a real boy. Jiminy, for his part, is awarded a golden badge as a sign of his amazing conscience capabilities.