Nandi is the bull vahana of Shiva. In many Shiva temples, Nandi is placed directly opposite the entrance to the shrine containing the central image of Shiva, the shiva linga. In this position, Nandi is acting not only as Shiva's guardian, but also as a constant devotee. As Nandi mimics the position of every devotee who comes to stand before the deity, he is often revered as a model devotee.
In the Panchanadha Shetram, Nandhi is described as a very staunch Shiva devotee who will never tolerate any unbecoming word about Lord Shia. Once during Daksha Yagna , Daksha spoke rudely of Lord Shiva and Nandi closed his two ears, chanting "Siva , Siva".
As an independent deity, the bull was known in ancient India as Nandikeshvara, the Lord of Joy, often represented as a man with a bull's head. Nandikeshvara was a rishi who offered service to Shiva by guarding his door.
Lord Shiva has various names describing his association with Nandi. Vrishavahanamurti, the form of Shiva resting against Nandi, is the form he assumes when blessing devotees with freedom from the cycle of existence.
Mahanandishwara is the presiding deity of Lord Shiva that resides in Mahanandishwara temple in Mahanandi. Within a 15 kilometer radius from the temple lie nine Nandis known as "Navanandis". Mahanandi temple is one of the Nava Nandis, and the other eight temples Prathama Nandi, Naga Nandi, Vinayaka Nandi, Garuda Nandi, Shiva Nandi, Vishnu Nandi, Surya Nandi, and Soma Nandi.