Lord Vishnu's Penance & Mel-Thali Origin Legend
According to the Kanchi Puranam, Lord Vishnu assumed the form of Mohini (the divine enchantress) during the cosmic distribution of Amritham (nectar of immortality) to deceive the Asuras. After the task was completed, Lord Vishnu desired to shed the Mohini form and regain His original masculine form (Purusha Roopam).
Lord Vishnu travelled to Kanchipuram, selected a peaceful spot on the western side of the town (Mel-Thali), dug the sacred Vishnu Theertham (Odha Ethi Theertham), and established a Shiva Lingam. He performed intense penance worshipping Lord Shiva. Pleased by Vishnu's sincere prayers, Lord Shiva manifested from the Lingam, restored Vishnu to His original divine form, and granted Him eternal peace. Since the temple was established on the western side (Mel = West, Thali = Temple), it came to be known as Thiru Metrali, and the presiding deity was named Sri Metrali Nathar.
Saint Sundarar's Gold Coin Miracle (Odha Ethiyappar)
When Saint Thirunavukkarasar (Appar) visited Thiru Metrali during his pilgrimage, he offered intense devotional service, sweeping the temple corridors and singing Tevaram hymns without asking for any material boons (Odhadhe Ethiadhar = Those who worship without reciting petitions). Later, when Saint Sundarar visited Thiru Metrali, he sang Tevaram verses describing Appar's selfless devotion.
Lord Shiva was so pleased by Sundarar's tribute to Appar that He miraculously granted bagfuls of gold coins (Pon) to Sundarar to support his pilgrimage and feeds for devotees. Because Lord Shiva granted boons to Appar and Sundarar even without them asking for material rewards, the deity earned the divine name Odha Ethi Eeswarar ("The Lord who bestows grace without being asked").