Nandi The Divine Bull
According to Some Puranas, he was born out of the right side of Vishnu resembling Siva exactly and given as a son to the sage Salankayana. Some purnas mention him as the son of the sage Silada who got him by the grace of Shiva.
It was Nandi who cursed Ravana (the demon King of Lanka) that his kingdom would be burnt by a monkey (Vanara). And later Hanuman burnt Lanka when he went in search of Sita, who was kept prisoner by Ravana in Ashok Vatika. 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 Nandis 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.
When the positive forces, the devas, and the negative forces, the asuras, joined together on a rare occasion to churn the ocean with a mountain to obtain the nectar of immortality they utilized Vasuki, the serpent, as the rope. The devas pulled from one end and the asuras from the other. Vasuki was upset during the process of this churning, and vomited up a poison which became human karma. This "poison" was so dangerous that none of the devas or asuras wanted to go near it. It was extremely sticky and coming into contact with this poison, i.e, human karma, would drag the divinity down to the realms of human suffering and ego. As everyone else ran away, Lord Siva, followed by Nandi, came forward to help as he was the only one who could counteract this deadly poison. Shiva took the poison into his hand and drank it. Nandi saw some of the poison spill out of Siva's mouth and immediately drank if off the ground. The devas and asuras watching were shocked and wondered aloud what would happen to Nandi. Lord Siva calmed their fears saying, "Nandi has surrendered into me so completely that he has all my powers and my protection"