Thomas Edison is most well known for his invention of the light bulb. Contrary to popular belief, Edison did not invent the light bulb; it had been around for a number of years. The electric lights at the time, however, were unreliable, expensive, and short-lived. Over twenty distinct efforts by other inventors the world over were already underway when Edison entered the light bulb invention race.
By creating a vacuum inside the bulb, finding the right filament to use, and running lower voltage through the bulb, Edison was able to achieve a light bulb that lasted for many hours. This was a substantial improvement, and one that led with more improvements, to making the light bulb practical and economical.
Of course, Edison also later invented the entire electric utility system so he could power all those light bulbs, motors and other appliances that soon followed.