The story
Brand name. Originally trademarked by the Rowntree's company in 1911. Apparently named after the Kit-Cat Club, which got its name from a local pastry chef, Christopher Catt/Catling (sources differ on the surname), who was nicknamed “Kit” and supplied the club with meat pies that he called “Kit-Cats”.
Etymology from Wiktionary, CC BY-SA 4.0.