In ancient times, there was a long and bitter fight between gods(devas) and demons(asuras). Ultimately the gods came off victorious, but thereafter they began to indulge in pride and became proud of their own prowess and possession of power. It is said that the Almighty, feeling that the god's pride must be curbed, incarnated himself as Yaksha or a super-mundane being who inhabits the upper regions, and as such Yaksha appeared before gods. Puzzled by his appearance and not knowing who he was, they deputed the god of fire(Agni) to find out who he was.
Agni proudly walked towards the Yaksha, and the latter asked him, “Who art thou?” Agni replied, “I am known as Agni and some people also call me Jatavedas.” “Why is thy power?” asked the Yaksha, and he replied, “I can burn anything in the world into ashes and none can escape me. “The Yaksha then placed a piece of dry straw before Agni asked him to burn it. Agni, however, tried with all his power to burn that wisp of straw but was unsuccessful. He was surprised at the failure of his powers and came back to the gods greatly crestfallen. The gods there upon sent Vayu(the god of wind) to meet the strange being. When Vayu met him, the latter asked again who he was and what he could do. Vayu replied, “I am the wind and I am also known as Matarishwan. I can blow away anything that comes in my way.” The Yaksha then placed the same wisp of straw and asked him to blow it away. Vayu tried with all his strength but couldn't move it from its place. This confused and puzzled him and he also returned to the gods amazed at the loss of his powers. Thereafter, the gods persuaded Indra to go and meet the Yaksha. As Indra approached the Yaksha, the latter vanished into the air. Indra stood confounded, when he saw the goddess Uma(Shiva's consort) appear before him in her resplendent beauty. Indra asked her reverentially, “Where is that wonderful being that was here a moment ago?” Uma said, “That was the form of the Almighty has taken. All of us exist on account of his being and it is to show you that your victory was due to his power and grace that he appeared before you and showed that without his aid none can claim any power as his own.”
Author: Swami Sambuddhananda
Source: VTS, Ref. Kenopanishad