The original four-finger version of the bar was developed after a worker at the Rowntree's factory, York put a suggestion in the recommendation box for a snack that a "man could have in his lunch box for work".  The product was launched in September 1935 in the UK as Rowntree's Chocolate Crisp, and the later two-finger version was launched on May 15, 1936.  Rowntree's Chocolate Crisp was renamed Kit Kat Chocolate Crisp in 1937, and after World War II just Kit Kat....

The original four-finger version of the bar was developed after a worker at the Rowntree's factory, York put a suggestion in the recommendation box for a snack that a "man could have in his lunch box for work".  The product was launched in September 1935 in the UK as Rowntree's Chocolate Crisp, and the later two-finger version was launched on May 15, 1936.  Rowntree's Chocolate Crisp was renamed Kit Kat Chocolate Crisp in 1937, and after World War II just Kit Kat.  The following advertizements ran from 1965-1969 and include the slogan, "Have a break…  have a Kit Kat." Corpus Corpse:  Wait for the break (1965) B&W Traffic Jam:  Have a break, have a Kit Kat (1965) B&W Lay By:  Have a break, have a Kit Kat (1965) B&W Cowman:  Have a break, have a Kit Kat (1965) B&W Crossword:  Have a break, have a Kit Kat (1966) B&W Dancing Class:  Have a break, have a Kit Kat (1966) B&W Gardening:  Have a break, have a Kit Kat (1966) B&W Sewing:  Have a break, have a Kit Kat (1966) B&W Crane:  Have a break, have a Kit Kat (1966) B&W Children:  Kit Kat makes the break that keeps you going (1967) B&W Demolition:  Kit Kat makes the break that keeps you going (1967) B&W Housewife:  Kit Kat makes the break that keeps you going (1967) B&W Production Line:  Kit Kat makes the break that keeps you going (1967) B&W Typing:  Kit Kat makes the break that keeps you going (1967) B&W Gardeners:  Kit Kat makes the break that keeps you going (1967) B&W Tent:  Kit Kat makes the break that keeps you going (1967) B&W Sailing:  Kit Kat makes the break that keeps you going (1967) B&W GPO Man:  Kit Kat makes the break that keeps you going  (1967) B&W Hairdressers:  Kit Kat makes the break that keeps you going (1968) B&W Decorating:  Kit Kat makes the break that keeps you going (1967) B&W Farmyard:  Kit Kat makes the break that keeps you going (1967) B&W Polishers:  Kit Kat makes the break that keeps you going (1968) B&W Moving Home:  Kit Kat makes the break that keeps you going (1968) B&W Tailors:  Kit Kat makes the break that keeps you going (1968) B&W Garden Shed:  Kit Kat makes the break that keeps you going (1968) B&W Petrol Pump:  Kit Kat makes the break that keeps you going (1968) B&W Gymkhana:  Kit Kat makes the break that keeps you going (1968) B&W Log Cutting:  Kit Kat makes the break that keeps you going (1969) B&W Switchboard:  Kit Kat makes the break that keeps you going (1969) B&W Fashion Show:  Kit Kat makes the break that keeps you going (1969) B&W Scramble:  Kit Kat makes the break that keeps you going (1969) B&W Cash Desk:  Kit Kat makes the break that keeps you going (1969) B&W