He was the first and foremost of the Saiva siddhantins. He was one among the eight saints who were enlightened by Nandi. Among the eight he alone preserved his enlightenment in writing. He was one among the greatest yogins, India has ever produced. His friends were Patanjali and Agastya who were also as great as Tirumular. His age is not definitely known. It is said that he was originally Sundarar of Himalayas. Sundarar came to Chidambaram in TamilNadu for worship. Because Chidambaram worship was considered very holy. He finished his worship and waited in Tamil Nadu for preaching Saiva System of worship. One day he happened to witness the tragic end of Mulan, a shepherd. He was driving the cows home. All of a sudden he fell down and died. The cows stood around the corpse and grieved the loss of their master. The Saye Sundarar was worried very much about the cows. Now the cows are rendered masterless and they shed tears. The sage now wanted to help the cows. He kept his body in a hollow of a tree and transmigrated his Atman to the body of Mulan. Now Mulan got up and the cows remained happy. He drove the cows home. Mulan's wife received him but he did no enter the house. He remained outside and slept in temple only and often entered into deep meditation. The villagers were astonished to see the strange attitude of Mulan first. Later they decided great inspiration had dawned on him. Mulan's wife left him and he wandered singing in praise of the Lord. It is said that he had lived upto 3000 years. It could be possible for him since he had been a great yogi. He had been a Sannyasin who knew all the eight siddhis. He is one among the eighteen siddhas. He meditated under a banyan tree in Thiruvavaduthurai and wrote 3000 poems one poem in a year.
His collection of poems is called 'Thirumantiram'. In Tirumantiram all yogas are explained Hada Yoga, Raja Yoga, Karma Yoga, Tantra Yoga, Mantra Yoga and Daya Yoga.