Lord Shiva's sacred Bull is the Hindu God Nandi
Accordingly Nandi is regarded as the gatekeeper and protector of Shiva as well as Shiva’s consort the Hindu Goddess Parvati. He can be found in many temples dedicated to Shiva throughout Asia seated and facing the main temple as protector. His name, Nandi, is even used as metaphor meaning “to stand in the way of”. It is said that one must first gain the approval of Nandi before being allowed worship of Lord Shiva himself.
Moreover he was said to be bull-data-faced with a body much like his hallowed Shiva, but with 4 hands. Two hands holding axe and antelope, and the other two joined in homage. In this human form he is known as Nandikeshwara.
It is said that many women visit these large Nandi statues outside temples
throughout the world and decorate him with flowers and touch his stone in
order gain fertility. Many worshipers who flock to his side also often
whisper to in him in order to announce their hopes and dreams hoping Nandi
relays their message on to Shiva.