El Cuco is believed to have been a sick man with tuberculosis. He became desperate for a cure and went to a curandera. There she told him that he must drink the blood of a child. He went out at night and kidnapped a 7 year old boy. He stuffed him in a cloth bag and slit his underarm and drank his blood.
It is said that he lurks the streets at night. He walks up and down the dark lonely streets in searched of kids who are misbehaving or roaming alone.
The moral of the story is to obey. This legend is passed down from generation to generation to scare misbehaving children. It is still relevant today because it's still told to fright children.