The microwave oven, aka the "Popcorn and Hot Pockets Warmer," was a happy accident that came from, of all things, a weapons program.
Percy LeBaron Spencer was a self-educated engineer working on radar technology in the years following WWII. The technology in question was the sci-fi sounding magnetron, a piece of machinery capable of firing high intensity beams of radiation.
Above: a scientist, with robot.
Apparently, P.L.S., as some have called him, had a bit of a sweet tooth. Or a strange fetish. Either way, he had a candy bar in his pants while he was in the lab one day. The self-proclaimed engineer noticed that the chocolate bar had melted when he was working with the magnetron.
Spencer disregarded the simple idea that his body heat had melted the chocolate in favor of the less logical and therefore more scientific conclusion that invisible rays of radiation had "cooked it" somehow.
A sane man would stop at this point and realize these magical heat rays were landing just inches from his tender scrotum. Indeed, most of the military experts on hand probably dreamed of the battlefield applications of their new Dick-Melting Ray. But like all men of science, Spencer was fascinated and treated his discovery like a novelty. He used it to make eggs explode and pop kernels of corn ("Imagine, a future where a building full of workers in cubicles eat this all day!")