What is the 4-letter word that rules the world?? (traditional story)

In a remote mountain village, the head of the village died and leadership was passed onto his son. Now the people had lived for many years under the control of a huge monster who loomed like a huge shadow over the village. Whenever anyone tried to find freedom, this large shadow appeared with a loud voice echoing through the mountain. The villagers always retreated at the sight of the dark image.

The young man who was was now the leader realised the time had come to confront this monster. He went out with a group of villagers and as soon as they appeared at the edge of the village, the huge shadow appeared. They stepped back in fright. 
The young man observed how the shadow became bigger and the voice louder as they retreated. He paused and then bravely took a step towards the shadow. It seemed to become slightly smaller. He stepped again and his view was confirmed as the shadow became less and the voice less powerful.
He continued moving towards it until the source of the shadow was at his feet. He plucked up this small ephemeral object in his hand and asked ‘Who are you?’
‘Fear’ was the weak, feeble reply. He closed his hand and it disappeared entirely.