Shiva, the Lord of Dance, is forever dancing his Cosmic Dance.
You’ve seen him as the Nataraja, lost in a trance, keeping the rhythm of the Universe with his dumroo( drum) and dancing to its beat.
Holding a trident in one hand, a deer in another, he is seen striking a beautiful pose with one leg lifted, the other placed on a dwarf. His matted locks, unfurled, spread out like rays reaching the outer edges of the Cosmos. As Nataraja, he shows us the cycle of life and death, Beginning and End.
There are times however, when Shiva will take on his Rudra avatar( Harsh Self) and dance the Tandav Nritya, the dance of destruction.
He dances at a furious pace,to the beat of his drum. Bom, Bom it vibrates, causing wild thunder storms all around the universe, even shattering the sun, the moon and other stellar bodies.
Brandishing his trident, he destroys Tripura, the three worlds. He tramples upon the dwarf of ignorance and conquers death, displaying its skull on his head.
But, for those who are dare to look at this terrible sight, he raises his right hand to say ‘be fearless’; for what is being destroyed is only your ignorance, you ego; the illusion that you are just this.
And then, if you pay close attention you will see a crescent moon shinning on his forehead, and you will know it is going to be light again and darkness will be gone. As your ignorance is destroyed,you will find enlightenment .
Thus, while Brahma creates the Universe and Vishnu drives it, Shiva destroys it, both within and without, so that it may be created again.
( The Tandav dance is often performed in Classical Indian dance forms. Here is great clip of Meenakshi, an Indian actress dancing it in a Bolywood movie)