Agasthya is one of the greates names in the Hindu Pantheon. He finds an important place among the Rishis, munis, and The Siddhars. He is also reputed to be the founder of the Tamil language which was taught to him by Murugan Himself. He drew up the first grammer rules for Tamil.
Agasthya was created in a pitcher - kumbha. He got the name Kumbha Muni, Kumbha Sambhava, and KalasOdhbhava from that reason.
During the marriage of Siva and Paarvathi, there was an over-crowding in Kailas in the north of the Bharatha Kantam. Because of this, the kantam tilted and sank in the north with an up-lift of the south.
Agasthya was asked by Siva to go to the south of Bharatha to counterbalance the over-crowding of the north.
Agasthya wanted to take a holy thirththa for his penance and ritual purposes. He was given the holy KAveri by Siva. KAvEri was accommodated in the kamandalu of Agasthya and he took it and started on his journey south.
As he proceeded, he approached the vicinities of the asura Kraunja. Kraunja was a master of illusions. The story has already been told briefly, before. Because Kraunja deluded him in the form of a mountain full of maze-like caves and entrapped Agasthya, Agasthya cursed him to remain in the form of a mountain. Then he came to the Vindhya Mountain.
Among the eight important Kula mountains called Ashta Kulaachalams or Ashta Kula Parvathams, Mount MEru was the prime mountain. Vindhya was one of the other seven. The planets went round the Meru in their paths.
Vindhya's jealousy towards MEru was provoked by the Sage Naaradha. Vindhya wanted to show his might and outdo MEru. So he grew and grew and grew. He grew to such dimensions that he stopped the planets in their tracks.
When Agasthya came to Vindhya, he saw the immense size of Vindhya which was blocking his path. Agasthya asked Vindhya to let him pass. But the haughty Vindhya told Agasthya to find his own way.
Hence Agasthya lifted up his hand. It grew and grew and grew. He raised his palm above the top of Vindhya and pressed him down. The immense Vindhya became flattened into a plateau. Vindhya asked for forgiveness and to be restored to his original size. But Agasthya simply answered, "When I come back", and went on.
Then Agasthya came upon the 'Terrible Two' - Vathapi and Ilvalan. He destroyed Vathapi and obtained immense riches from Ilvalan for his marriage with LOpAMudra.
Sages had to marry and have Rishi pathnis. They had to have children who would be raised in the path of Dharma, divinity, and tapas. Failure to produce offspring would cast them in a special form of hell called 'Puth'. A man had to make offerings to his ancestors.
Having a son, would prevent a person from going to the 'Puth' hell. That is why a son is known as 'Puthra'.
So, Agasthya created a most perfect girl whom he named 'LOpAMudrA' and left her in the custody of the King of Kasi, until he came to marry her. He duly married her, thereafter.
LOpAMudrA is a female Rishi. There are twelve schools in the SriVidya upaasana maarga - worship of AmbaaL. Among them, Agasthya propounded one school. LOpAMudrA has initiated another. The importance of Lopamudra is illustrated well in the Sri Lalitha Trisathi.
Agasthya wanted to be initiated into the Path of SriVidya - Worship of the Mother Goddess as Sri Lalitha/Rajarajeswari. So he approached SriHayagriva who is a manifestation of MahaVishnu. Hayagriva has the head of a horse, is four-armed with shanka, chakra, gatha, lotus, SriVatsa, Kausthubha, and PIthAmbara.
SriVidya Path considers Hayagriva as the prime praeceptor of the marga. Hayagriva taught many things to Agasthya about SriVidya and finally culminated with a rendition of the SriLalitha Sahasranama.
Because Agasthya was the husband of LopAmudra, the Great Goddess Herself recommended to Hayagriva to initiate Agasthya into the SriLalitha Trisathi pujai. Both of them have worshipped Sri Lakshmi of Kolhapur and have given us the MahaLakshmi SthOthram' which is hailed as the 'Selva ThiRavu KOl' in Tamil.
Agasthya, then continued south, until he came to the Sahyaadri Mountains. Just before that time, Indra was hiding in Siirgaalzi within the strand of a fibre in a lotus stalk. He had to perform a penance towards Siva. For that, he had to have a special holy thiirththam.
Indra was advised by Naaradha to pray to Vinnayaka to bring a holy thiirththam to Siirgalzi - in this case the KavEri in Agasthya's kamandalu.
Vinnaayaka took the form of a crow and perched on the kamandalu of Agasthya when Agasthya was meditating. When Agasthya realised this, he shooed away the crow. But the Divine Crow tipped the kamandalu and toppled it. Out, poured Kaveri which started flowing. The crow disappeared and in its place stood a small boy. Agasthya thought that the boy was playing some prank and clenching both his fists, went to pound the head of the small boy. But the boy escaped and Agasthya gave chase. Finally the boy vanished and Vinaayaka showed Himself to Agasthya. Agasthya was aghast at the realisation that he had just tried to knock the head of Vinaayaka Himself. As atonement, he knocked his own head with both of his clenched fists.
This became the 'PiLLaiyaar Kuttu' which is an integral part of Vinaayaka worship.
Kaveri flowed towards the place where Indra was doing penance and flowed out into the Eastern Sea and thus became a Holy River of TamilNaadu. Vinayakar scooped up some Kaveri water with His trunk and poured it into the kamandalu of Agasthya.Then Agasthya proceeded further.
Agasthya then went to KuRRalam where he was prevented by the Vaishnavas from entering the temple because he was a Saivaite. But he caused the statue of Vishnu to turn into a SivaLinggam and performed his puujai there.
After that, he settled himself at the Sahya Mountains which are known as the Podhiyil Mountains or Malaiyamalai and wrote out the grammar for Tamil with the help of Vinayakar. AruNagiri Nadhar has mentioned in his ThiruPugalz -
"muththamilz adaivinai muRpadu girithanil muRpada elzudhiya muthalvOnE!"
He was involved in the First Tamil Sangam. The grammer works by him were named after him as 'SiRRagaththiyam' and 'PEragaththiyam'. There were lost except for some scanty references to some verses from them.These verses are found as references and quotations.
The Sage Agasthya remains as the founder of Tamil language which was Taught to him by Murugan Himself.
That is why Murugan is known as the Tamil God.
And Agasthya is known as the Tamil Muni.