Nandi is the bull associated with Shiva. The story of the
birth of Nandi begins with Sage Shilada doing intense penance to be blessed
with a child. He offered the prayers to Indra, the king of Devas.
When Indra appeared before him, Sage Shilada prayed for a
son who would be immortal. But Indra was incapable of granting such a boon and
so he asked the sage to pray to Shiva.
Sage Shilada performed intense penance for several years.
The tapas was so intense that he was reduced to a bony figure.
Finally Shiva appeared and gave the boon that He Himself
will appear as his son. To get the son, He asked the sage to perform a yajna.
The sage performed the yajna and at the end of it a child
appeared from the fire.
As the child brought joy and happiness to everyone, he was
called Nandi.
The sage took the child to his hermitage. But the child did
not show any signs of his divinity. He moved around like an ordinary child.
One day Mitra and Varuna, Vedic gods, visited the ashram and
told the sage that the child will not live beyond the age of eight years.
The sage was saddened but Nandi who came to know about his
fate offered prayers to Shiva.
Shiva appeared before Sage Shilada and Nandi and told
that the child is immortal as he will be always staying near him. Shiva took
off his necklace and gave it to the child.
As soon as the child wore the necklace, Nandi assumed his
divine bull form. He became one of important Ganas. Nandi is thus always
present where there is the presence of Shiva.