The term Tripurari translates as the destroyer of the three cities. Let us go through the interesting mythological story narrating how Lord Shiva got this title.
The store behind the name
Once there were three powerful demons called Kamalaksha, Tarakaksha, and Vidyunmalin who were blessed with three flying fortified cities made of gold, silver and iron respectively. The three demons were so arrogant and horrible that they caused havoc in the three worlds. They would fly freely anywhere they wanted and would land their cities on gatherings and crowds to crush the people to death. They enjoyed all their horrible deeds as fun. The gods had vacated the heavens and had disappeared into unknown places. There was terror everywhere. When the gods, humans and the celestial forces prayed Lord Shiva to intervene in the matter and do something about the demons, Lord Shiva compassionately accepted to put an end to the atrocities caused by the evil-minded asuras.
Lord Shiva turned the two mighty mountains Gandhamadana and Vindhya as the two poles of his chariot. The earth with its oceans and forests became the chariot. The gigantic snakes namely the Sesha became the pivot of the chariot with moon and sun as the two wheels. Elapatra and Pushpadanta snakes became the two pins of the yoke with the Malaya Mountain becoming the yoke. Snake Dakshaka tied the yoke to the poles. The four Vedas became the four steeds with the supplementary texts becoming the brittle bits. Gayatri and Savitri became the reins and the syllable OM the whip and Brahma the driver of the chariot. The Mandara Mountain became the bow with snake Vasuki as the string. Lord Vishnu became the shaft of the arrow with Agni as the arrowhead and Vayu as the two wings of the shaft and Yama as the feathers in the tail. Lightning became the whetting stone and Meru the standard. Thus all the celestial forces united together to construct the mighty chariot rode by Shiva.
In a cosmic war against the three demons, their cities were shattered and the demons were killed by Lord Shiva. Once again peace ruled over the three worlds with all the gods and celestial forces assuming back their regular responsibilities. The mighty divine mission won the title Tripurari to Lord Shiva as He put an end to the three cities. This is yet another instance to praise the valor, power, and compassion of the Lord.