In Hinduism, Agastya (अगस्त्य in devanagari, pronounced /ə gəs tyə/) is a legendary Vedic sage or rishi. Agastya and his clan are also credited[who?] 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 Supreme Brahman. 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 Arjuna and Ashwatthama at the end of the war).
Humbling the Vindhya mountains
Legend says that the Vindhya mountains that separate north and south India from each other once showed a tendency to grow so high as to obstruct the usual trajectory of the sun. The need arose to subdue, by guile, the Vindhyas, and Agastya was chosen to do that.
Agastya journeyed from northern solstice to southern solstice, and on the way encountered the now impassable Vindhya mountains. He asked the mountain range to facilitate his passage across to the south. In reverence for so eminent a sage as Agastya, the Vindhya mountains bent low enough to enable the sage and his family to cross over and enter south India. The Vindhya range also promised not to increase in height until Agastya and his family returned to the northern solstice. Agastya settled permanently in the south, and the Vindhya range, true to its word, never grew further. Thus, Agastya accomplished by guile something that would have been impossible to accomplish by force. Ramayana covers this astronomical correction made by Rishi Agastya. It is from here that the science of Vastu Shastra originated.
Agastya and Lopāmudrā
As with all other Hindus, it was necessary for Agastya to marry and sire a son, in order to fulfill his duties to the Manus. Once he resolved upon doing this, Agastya pursued an unusual course of action: by his yogic powers, he created a female infant who possessed all the special qualities of character and personality that would be appropriate in the wife of a renunciate. At this time, the noble and virtuous king of Vidarbha (an area in south-central India, just south of the Vindhya mountains), was childless and was undergoing penances and prayers for the gift of a child. Agastya arranged for the child he had created to be born the daughter of that noble king of Vidarbha. The child was named "Lopamudra" by her parents. Upon her coming of age, Agastya approached the king and sought the hand of his daughter. The king was initially chagrined to hear such a suggestion from a renunciate, but found that his daughter, who had early exhibited extraordinary standards of mind and character, was insistent that he should accept the proposal. She was utterly intent upon exchanging the palace of her father the king for the forest-hermitage of Agastya. Lopamudra and Agastya were duly married and lived a life of extraordinary felicity. It is believed that they had two sons - Bringi & Achuthan.
Legends about Agastya
One story about Agastya goes that once the demons had taken refuge in the ocean and it was difficult for the gods to vanquish them, so they went to Sage Agastya for help. Then, after hearing the gods, the sage drank the entire ocean water and held it within him until the demons were destroyed. After the demons were destroyed, Devtas requested him to save the sea animals who were dying because of lack of water. At Devtas request Agastya Rishi released all the water as urine and that is why the sea water became salty.
Agastya is said[Please name specific person or group] to have "dedicated" all the forest animals to the deity Rudra hence making them fit for eating if killed while hunting. Agastya is famous for being the first siddhar in the siddhars tradition. He created many medicines, and jadhakam, mandhrikam and he said all of them.
In his book, he gives description of, and instructions for the creation of medicines for fever(it may be of any type), cancer, treatments for impotence, abdominal problems, brain and eye problems, bone problems, etc. Reputedly, his medicines give quick results without any side effects.
Vathapi Legend about Agastya
Another story has it that two demon brothers, Ilvala and Vathapi, used to kill people who were passing by the forest in a special manner. Vathapi was good at changing to other life forms and the other, Ilvala knew the supernatural slogan Sanjivani mantra which, when invoked can bring back a dead person to life. They hatched a plan against Agastya that Vathapi would turn into a goat and be killed and fed to Agastya. After Agastya had eaten the meat, Ilvala would invoke the Sanjivani mantra to bring back his brother Vathapi to life, who in turn would rend Agastya's stomach and come out thereby killing him. By the plan, one changed into a goat and the other disguised himself as a Brahmachari who invited Agastya to a meal. Agastya knew beforehand about the plan due to his immense Vedic powers, but he resolved to teach both a lesson. After the meal, Agastya simply rubbed his stomach saying Vathapi JeerNo bhava; literally may Vathapi be digested, while the other demon tried to bring his brother to life in vain. Agastya plainly informed the demon that his brother has been digested and could no longer be brought back to life.
Other facets of Agastya
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[Please name specific person or group] 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. Another story about him is that once when the great sage accompanied by his beloved royal wife were wandering through forests, she fainted due to the humidity and hot conditions prevailing in the south. She was royal, hence not exposed to hard conditions. By seeing this the great sage became angry and prepared to punish the Sun God with his bow and arrows. Upon seeing this the sun god feared and appeared before Agastya and presented him with umbrella and chappals (foot wear).
Unity of Vishnu and Shiva
At a Saivite temple named Kutralam, formerly a Vishnu temple, in Tamil Nadu, Agastya, in one legend, was refused entry. He then appeared as a Vaishnavite devotee and is said to have miraculously converted the image to a Shiva linga.A symbolic meaning of this conversion is to show that Vishnu and Shiva are different aspects of the one and same God.
Agastya In Akilam
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.
So as per Ayyavazhi, in Kali Yukam all the knowledge, including the basic formulae and forms of modern scientific technologies came from Agastya.