Step 1 : Introduction to the question "Who invented the first modern chemical-based handheld fire extinguisher?"
...It's a good thing we're being specific, because people have been finding ways to extinguish fire since the discovery of...uh...water. But though there had been some attempts before him, it was Captain George William Manby of the Cambridgeshire Militia in England who would help firefighters take that major leap. He developed the pressurized extinguisher that would spray a potassium carbonate mixture to keep blazes at bay in 1819. He was also a pretty interesting dude in his own right, inventing other life-saving devices and hobnobbing with the man who would become Lord Nelson. Source: The Fire Safety Advice Centre, Norfolk Museums