Thomas Edison. Say what you will about how he stole a lot of stuff from his flunkies and rivals, but one of his contributions was the big one, and was genuinely his.
Edison invented the industrial laboratory.
An industrial laboratory is what turns an invention into a product. It refines a proof of concept to an item that people would use in a practical setting, and in a form that may be mass-produced. It's what turns an idea that might change your life into something that does change your life, on a massive scale. Nikola Tesla might have been long on bright ideas, but very short on business sense; his inventions got nowhere until Edison's industrial laboratories refined them into products. The light bulb was a bright idea, but it took Edison to pore through thousands of materials to find out the right material for that filament, and to realize that the best way to maintain the life of the bulb was to fill it with an inert gas, not leave it as a vacuum.
Without the industrial laboratory, the modern world would not exist. Full stop.