Anyone visiting a temple of Lord Śiva will not miss the image of a reclining bull, generally facing the Śivaliṅga in the sanctum. This bull is called by various names such as Nandi, Nandīśvara or Nandikeśvara. It is the vāhana or mount of Lord Śiva even as the Garuḍa (eagle) is the vāhana of Lord Viṣṇu.
There are several stories in the purāṇas about this Nandikeśvara.
A sage, Śālaṅkāyana by name, performed austerities to get a worthy son. Pleased with him, Viṣṇu appeared before him; and lo! a baby figure exactly like Śiva emerged out of him. This was Nandikeśvara.
According to another legend, the sage Śilāda performed a yajña to get a son who would be immortal. A brilliant lad, resembling Śiva, suddenly appeared from the inner apartment of his house. He was Nandikeśvara. Another story states that sage who performed severe austerities on the Muñjavān peak of Mandara mountain was made the chief of his attendants by Śiva, who gave him the name Nandīśvara or Nandikeśvara. Iconographically, Nandi-keśvara is shown either as a small reclining bull facing the Śivaliṅga in the sanc-tum or as a big bull in a separate maṇḍapa (hall) with elaborate workmanship, either facing the main shrine or the main gate.
In many temples, especially in Tamil Nadu, Nandikeśvara is shown in the human form, either with a bull’s head or a human head with jaṭāmukuṭa. (See JAṬĀMUKUṬA.) He may have three eyes and four arms, the back hands holding paraśu (axe) and mṛga (deer) and the front two folded in supplication (añjalimudrā).
Nandikeśvara is said to have cursed Rāvaṇa to be destroyed by monkeys when he once ridiculed him near the Kailāsa mountain (Rāmāyaṇa, Uttarakāṇḍa 16).
The image of Nandikeśvara should be stationed at the dakṣiṇadvāra or southern door of the temple.
See also ADHIKĀRANANDI.