Hi Zephyr......welcome to TFF
"When was the idea of a multiple shot fire arm introduced or even thougt of?"
Probably when the first guy who shot a firearm tried to reload it in a hurry.
Seriously.....there were a number of attempts to build multiple shot firearms around the time of the American Revolution. Most involved fixed or revolving multiple barrels. The big hangup was the cumbersome flintlock ignition system.
With the coming of the percussion cap, it became somewhat easier. A number of guns with hand revolved cylinders and hand revolved barrels were tried until Sam Colt invented a simple, reliable internal mechanism for revolving and locking a multiple charged cylinder.....the first real revolver.
The invention of the self-contained cartridge opened up a whole 'nother range of possibilities......revolving weapons such as the Gatling Gun, the lever action, bolt action, pump action and various semi-automatic and automatic actions.