Who is Kovalan and Kannagi from Gods, Demons, and Others and what is their importance?

Kovalan and Kannagi are a married couple. Sadly, Kovalan indulges in an affair with a prostitute and loses their fortune, so they must leave their town of Puhar for the neighboring Madurai. The only thing of value the couple has left is a pair of very fine gold anklets. When Kovalan goes to sell them to the local goldsmith, the goldsmith, who'd recently stolen a fine gold anklet from the queen, was happy to meet Kovalan so that he could take his anklet, call him the thief, and kill him. When Kannagi hears of this outrage, she sets the town of Madurai on fire with her anger (literally). Finally, her anger is quelled when the city's deity comes to explain that Kovalan was paying for his actions in a previous life. She and Kovalan are reunited in the afterlife, and a temple to Kannagi is built on the spot where she and Kovalan ascended to heaven.