Agastya or Agathiyar  was a Vedic sage or rishi. Agastya and his clan are also credite   to have "authored" many mantras of the Rig Veda, the earliest and most revered Hindu scripture, in the sense of first having the mantras revealed in his mind by the SupremeBrahman. Agastya is also the author of Agastya Samhita. In some reckonings, Agastya is the greatest of the Seven Sages or Saptarshis. The word is also written as Agasti. A-ga means a mountain, Asti, thrower. Also a name of Lord Shiva.

Agastya the Rishi, was born of both Gods, Mitra and Varuna, from Urvashi. Agastya is also the Indian astronomical name of the star of Canopus, is said to be the 'cleanser of waters', since its rising coincides with the calming of the waters of the Indian Ocean. Another reference is in the Mahabharata in Sauptikaparva as the teacher of Guru Drona, who gave Drona, the greatest of weapons, Brahmastra (used by both Arjunaand Ashwatthama at the end of the war).He is considered as the first and foremost Siddha. He is considered the guru of many other Siddhas. He is also called Kurumuni, meaning short (kuru) saint (muni). He made contributions to the field of Medicine and Astrology - especially Nadi astrology. He is said[Tamil sidhhars] to have lived for over 5000 years, and that one of his medicinal preparations, Boopathi Kuligai, is so powerful that it can even bring the dead back to life. Two of his students and disciples were Therayar and Tholkappiar.

According to Akilattirattu Ammanai, the religious book of Ayyavazhi, Agastya was created from the mind of lord Siva inorder to offer boons to Kaliyan (See:Boons offered to Kaliyan). As per the order of Siva, Agastya offered many boons including all worldly knowledge to him.