Matsyendranath is one of the foremost teachers of the Nath tradition and he is the Guru of Gorakhnath, the founder of the Natha tradition. Matsyendra was the first human being who brought down the secret of Yoga for the benefit of humanity from Lord Shiva. The story of Matsyendranath has numerous hidden symbolism.
Legend has it that Matsyendranath started life as a fish in the ocean. He lived in a small pond in an island.
One day Goddess Parvati wanted to know the reason for the existence of the world as experienced through the senses.
This was a deep and profound knowledge. Shiva did not want to share it with anyone. But he could not displease Mother Goddess, so to enlighten her she took her to an island.
The only inhabitant of the island was a fish who lived in a pond. The fish overheard Shiva revealing the secrets of Yoga to his consort, Goddess Parvati on the uninhabited island. Creation, dissolution, transformation, the illusion all were discussed by Shiva and Shakti.
As he metamorphosed from fish, he came to be known as Matsyendranath.
He later had eight disciples who carried the teaching of Shiva to the eight corners of the world.
This story is found in the Navnath Charitra.