Among the eighteen Siththars, Agathiyar was the most renowned Siththar. He was known to have links with Gods and kings. He was also a legend in Sidha Maruthuvam.
Many references about Agathiyar can be seen in ancient Tamil songs, devotional literature like Devaram, and Vedas. He was also known as one of the seven rishis of Vedic period. Apart from this there are also several folk stories about him.
He managed to lead austere life inspite of being married. His wife name was Lobamuthirai and his son name was Sankaran.
In his book Samarasa Gnanam, he clearly explained about the important nerve knots of human body. Agathiyar ainthu saathiram, Agathiyar kiriyai nool, Agathiyar attamasithu, Agathiyar vaithiyarathna surukkam, Agathiyar vagada venba, Agathiyar vaithiya koumi, Vaithiya rathnakaram, Vaithiya kannadi, Vaithiyam 1500, Vaithiyam 4600, Senthooran 300, Mani 400, Vaithiya Sindhamani, Karisilpachyam, Naadi sasthira pasani, Pasmam 200 and medicinal books Perunthirattu, Sivasaalam, Dakthisaalam, Shanmugasaalam, Aarezhuthu andhadhi, Karmaviyaapagam, Vithi noon vagai kaandam, Agathiyar pooja vithi, Agathiyar soothiram 30, Agathiyar gnanam are some important books written by him.
Agathiyam, a book on Tamil grammar and Agathiya samhithai, a north Indian book was also said to be written by him.