A pair of old Charriot Nandis from Tamil Nadu

Nandi serves as the mount (Sanskrit: Vahana) of the god Shiva and as the gatekeeper of Shiva and Parvati. In Hindu Religion, he is the chief guru of eighteen masters (18 Siddha) including Patanjali and Thirumular. Temples venerating Shiva display stone images of a seated Nandi, generally facing the main shrine. There are also a number of temples dedicated solely to Nandi.

In one puranic story, it is stated that once Siva and Parvathi were playing a game of dice. For any game there has to be an umpire, who has to declare who is the winner. Siva and Parvathi agreed to have Nandi (the divine bull) as the umpire. Nandi is a favorite of Siva, as he is Siva's vehicle. Although Siva lost the game, Nandi declared him the winner. It is stated that Parvathi was indignant over Nandi's partiality for Siva and cursed him that he should die from an incurable disease. Thereupon Nandi fell at the feet of Parvathi and pleaded for forgiveness. "Mother forgive me. Should I not show at least this amount of gratitude to one who is my master? Is it not humiliating for me to declare that my master has lost the game? To uphold his honor I no doubt uttered a lie. But am I to be punished with such severity for so small an offence?" Nandi prayed for forgiveness in this manner. Parvathi forgave Nandi and taught him the means to atone for his lapse. She told him. "The Chaturdasi day in the month of Bhadrapada is the day when my son's birthday is celebrated. On that day you have to offer to my son what pleases you most (green grass)". This means that one atones for one's sins when one offers to the Lord what is most pleasing and enjoyable to him. For Nandi the most enjoyable and relishing food is green grass. As directed by Parvathi Nandi worshipped Ganapathi by offering green grass. Nandi was then relieved of his dreaded disease. His health improved and by the grace of Parvathi he was redeemed.