Agathiyar is mentioned as one of the Saptarishis and the foremost of the Siddhars. It is mentioned in the Rig Veda that Agathiyar was the son of Mithra Varuna and the brother of the visitor. Since everyone came to the north to see Lord Shiva's wedding, the north would go down without balance.
He came to worship Lord Shiva on the Bodhi Hill and perform penance. Later, Sundaranar met Yogamuni and Konkanar and consecrated Lord Shiva in their ashram and enjoyed the wedding of Lord Shiva, whom he could not see. History says that he learned Tamil from Lord Shiva and wrote the first Tamil grammar book called "Agathiyam".