The story
Term attested since at least the 1780s in the expression grin like a Cheshire cat. The reason why Cheshire was combined with cat is disputed: see here for more information.
Etymology from Wiktionary, CC BY-SA 4.0.
Cheshire cat
Chesh·ire catToday it means: A fictional cat with a broad fixed grin, made popular by Lewis Carroll's Alice's Adventures in Wonderland (1865). Full definition →