In Pandora Hearts, the Cheshire Cat, also known as the Smile Cat, is a powerful and enigmatic Chain originally created from the soul of a black cat who was the beloved pet of Alice one hundred years before the main story. As a cat, he was killed by Vincent Nightray, who used scissors to stab out his eyes. After his death, his soul was taken to the Abyss where he was transformed into a Chain by the Will of the Abyss, who is also known as White Alice. She granted him a near-human form, though he could not receive new eyes at first; she later remedied this by taking the left eye of Kevin Legnard, also known as Xerxes Break, and giving it to the Cheshire Cat, noting that its red color suited him.

The Cheshire Cat appears as a young man with shaggy black hair and cat-like ears, possessing oversized, powerful black arms that end in large claws. He wears a high-collared sleeveless shirt and a black cape, and his most treasured possession is a golden bell tied around his neck with a red ribbon, which contains the painful memories of White Alice that she wished to forget. His personality is defined by his single-minded and obsessive devotion to White Alice, whom he considers his master and the most important person in his existence. While he was affectionate and loyal to White Alice when she inhabited her sister's body, he deeply dislikes and avoids Black Alice, the core personality who interacts with Oz Vessalius, viewing her as a separate and unwelcome entity. His way of thinking is simple and instinct-driven, typical of a cat, and he often refers to himself in the third person. Although driven by a fierce and aggressive loyalty, he can also be cowardly, preferring to isolate his enemies in his own dimension to deal with them indirectly rather than facing them head-on in a fair fight.

Motivated by a fervent desire to protect White Alice from any kind of sorrow or pain, the Cheshire Cat takes on the role of a self-appointed guardian of her fractured memories. He resides within a dimension constructed from these memories, where he attacks anyone who attempts to recover them, including Black Alice and Oz. His logic is that by preventing Black Alice from regaining these memories, he can spare White Alice the anguish associated with them, even if it means killing his former owner. His central role in the story is that of an antagonist protecting the secrets of the past, forcing the main characters to confront him to obtain the truth of the Tragedy of Sablier. He is a unique Chain who does not require a contractor to exist in the real world, demonstrating his special nature.

His most significant relationship is with the Will of the Abyss, to whom he is utterly loyal, acting as her most faithful knight. In stark contrast, he holds Black Alice in contempt, perceiving her as a threat. His relationship with his former owner, Black Alice, is complex and initially hostile, defined by his rejection of her. His other key relationship is with Xerxes Break, from whom he received his left eye; this connection culminates in a brutal confrontation where Break deals him a near-fatal wound and shatters the bell containing White Alice's memories. Over the course of the narrative, the Cheshire Cat undergoes significant development. Though seemingly destroyed by Break, he does not completely disappear, instead wandering through the cracks between dimensions to heal. He reappears late in the story, having secretly observed all the unfolding events. When he learns that Glen Oswald intends to kill Lacey, an act that would prevent Alice's birth and destroy the Will of the Abyss, he intervenes directly. In a final, selfless act, he abandons his earlier hostility and accepts Black Alice as simply Alice, protecting her and ultimately choosing to fade away and disappear from existence together with White Alice.

The Cheshire Cat possesses a range of notable abilities befitting a powerful Chain. One of his primary powers is the manipulation of space and time, allowing him to create barriers and pocket dimensions that trap individuals within reproductions of their own memories. He can travel between any existing dimensions at will and teleport himself freely, often using his ribbon to facilitate this movement. Unlike other Chains, he does not need a contractor to leave the Abyss and manifest in the real world. He is capable of shapeshifting, able to take on his original form of a simple black cat, a more ethereal form consisting of a floating cat's head made of smoke with a wide grin, and a massive, gargantuan true form of an anthropomorphic cat over fifty feet tall that he resorts to only in the most dire of situations. He possesses enhanced speed, strength, and endurance, as well as a powerful regenerative healing factor that allows him to recover from wounds that would destroy other Chains.