It is believed by his devotees that this Hindu God could vary the intensity of this graceful and artistic dance to express the mood swings that were overtaking him quite often; it is also believed that the complete cycle of creating, preserving and dissolving in this world has its source in the Thandavam.
His Rudra Roop is the intense version of his personality, it is also full of violence and even the gods used to run away when he was in that fiery rage; he himself is the creator and destroyer too and, he is capable of destroying death itself. When he assumes the Rudra Roop, he starts performing the Taandava Nritya which is known to be accompanied by a stotra which is a eulogy or hymn that is sung along with the Tandava nritya
The other milder and joyous version of the Tandava is called Ananda Tandava which the lord used to indulge in when he was in a happier, more pious or sexually aroused mood
Shiva is describes a s Nataraja as per the Shaiva Siddhant traditions and he is the supreme lord who invented the Taandava and its various branches; hence, he is the King of Dancing.
The name of the dance is derived from the closest disciple of Shiva who was called Tandu; he was so adept at his knowledge of the dance form that he was the one who coached Bharata, the famous author of the Natya Shastra, a book that goes deep into the world of dance and its teaching. In doing so he also imparted a deep insight about the finer aspects of the Thandavam particularly in the usage Karanas and Angharas modes of the Thandava.
He has done this in compliance to the instructions of Shiva but there is also a thinking in some scholars that the Natya Shastra also contained an earlier work which might have been written by Tandu himself.
It is also believed that almost all the art forms of classical dance, music and song have been derived from the rituals and mudras derived from the Shaiva traditions.
Raavan Tandava Strotra
In fact there is an interesting story concerning the strotra that is sung along with the Thandav nritya; it concerns Ravana who is said to have been the one who created the Raavan Tandav Strotra which was sung by him as a prayer to Lord Shiva.
It is said that Ravana was a byproduct of the union of both the gods and the demons and he was blessed with the good qualities of both; the result was a personality, mind and body that was second to none in terms of the divine powers that he possessed. These powers kept on growing and he developed an awesome personality bestowed with all the right qualities.
With strict penance and meditation, he was able to please Lord Brahma who rewarded him with some weapons while also granting him invincibility. This boon and its ramifications went to his head and he went to Mount Kailash and uprooted it from the earth.
This affront offended Lord Shiva who used his toe to push down the mountain entrapping Ravana and started to crush him slowly. Sensing the extra pressure that was gradually increasing, Ravana found himself unable to contain the massive weight of Mount Kailash.
Realizing that he had made a huge mistake, Ravana started to plead for his life and sing praises to the almighty lord to spare his life even though he was an ignorant person.
But, what emerged from his learned entreaties was a wonderful form of poetry that was in the form of a prayer to the great qualities of Lord Shiva to invoke his goodness to spare his life; this prayer is known as Ravana Tandav Strotra. Since that time the strotra is sung along with the Tandav nritya to invoke the forgiveness and blessings of the Lord.
In turn, Lord Siva was really impressed by Ravana’s artistic talent in coming up with an extempore work of excellence that he pulled him out from under mount Kailash and rewarded him with a Chandrahaas which is a weapon.