According to the ancient Greeks, Prometheus took pity on mankind. He walked among men and noticed that they were no longer as happy as they were when Kronos the Titan was their king. He saw them living in the dark and shivering in the cold because they had no light to help them see and no fire to help them stay warm.
So Prometheus stole a spark from Zeus’s own lightning and brought fire to mankind. It was the dawn of civilization and enabled mankind to flourish.