The Cheshire Cat is an enigmatic being with no definitive origin. What is known is that it is a being that is able to disappear and reappear at will by separating its molecules apart and literally become nigh-omnipresent in the process. The Cheshire Cat has also shown that it can skillfully leave behind certain parts of its body, most notably its wide and rather disturbing toothy grin. The Cheshire Cat can also assume other different forms associated to camouflage and can even change its voice or mimic the voice of other characters.
The Cheshire Cat is widely known in the popular story of Alice in Wonderland where the main protagonist known as Alice encounters the feline sitting atop of a tree branch and becomes rather enamored by the creature's personality. There, the Cheshire Cat shows that it has a rather philosophical persona but speaks in riddles and often gives Alice many cryptic messages. While frustrating, they were shown to aid Alice in her endeavors near the end of the book.
Despite its origins being a mystery, there are theories as to how or where the Cheshire Cat was made. One theory suggests that the Cheshire Cat manifested into our plane of existence when the Jabberwock was let loose upon the human world driving everyone to utter madness and later on consuming them. While some have gone mad to the point where they would be institutionalized, others were insane on a nihilistic or existential level. From there, the Cheshire Cat spawned from such insanity; although the cat appears to speak in a posh and calm manner despite this.
Another theory suggests that the Cheshire Cat was once an ordinary house cat who was purchased by a scientist. This scientist in question was studying lobotomy but not for health reasons, rather to explore the depths of the human psyche and what lies beneath. After years of experimentation on human test subjects in believing that the deteriorating human brain can lead to certain realms, the scientist decides to perform the experiment on the cat. However, this resulted in the Cheshire Cat being born after it somehow was able to delve straight into that very psychic realm (Wonderland) and escaped there through unknown means, likely teleportation.