He was the author of the Yoga-Sutras that have his name: Yoga-Sutras of Patanjali; written around 150 BC. Nevertheless, those sutras have a great influence of Buddhist and Samkhyan ideas plus the sacred teaching of the Bhagavad Gita.
What yoga did Patanjali practice? Why is he depicted as a serpent?
PATANJALI AND RAJA YOGA (ASTHANGA YOGA)
The definition of yoga given by him is: योग: चित्त-वृत्ति निरोध: (yogaś citta-vṛtti-nirodhaḥ) - Yoga Sutras 1.2 Swami Vivekananda translates the sutra as "Yoga is restraining the mind-stuff (Citta) from taking various forms (Vrittis)." In other words, yoga is the science that controls the mind so it keeps steady or quite.
A way to explain this is as follows: Let us picture a raining day, full of clouds and because of that the city is in darkness. Where is the light? Where did it go? It did not go to any place. It is where it always is, right? The sun, light, is always over the clouds. The clouds are covering it and the city is in darkness, but the light still there. The sun is Atman. He is always there. What are the clouds? They are the thoughts. The more thoughts we have the more darkness we have. We get access to the light, Atman, by controlling our thoughts, the mind.
This is telling us something very simple: Meditation is the heart of Yoga. Yoga needs meditation because the latter is the technique to relax the mind to go beyond it, beyond the clouds.
WHO WERE THE PARENTS OF PATANJALI?
We can see that Patanjali’s lineage was very high. His parents were really special and so was he.
Patanjali got married to Lolupa and they had a son: Naga Putra (Son of the serpent). It is easy to understand that Patanjali had a great and special knowledge. He was a disciple of the serpent, the Kundalini and from it comes the name of his son.
PATANJALI AS A SERPENT!
The nagas were serpent deities and Sesha or Seshanaga was their king. Depicting Patanjali as a serpent indicates he was a Master who really knew about the control of the energies (Kundalini). Remember he was married and had a son because he was practicing Tantra Yoga, the science of sexual control. The idea of being single for ever has not a solid base, because sexual activity is part of nature. Freud teaches us that the base of our behavior is sex.
It is easy to control oneself being single, but… what about being married? It is for real yogis who want to become serpents, nagas.
WHY WAS PATANJALI BORN?
Vishnu asked Shiva to let the desire of Ananta to come true. Shiva let Párvati, his wife, to be born as Gonika and give birth Ananta in Kama Loka (Kama = desire, Loka = world). Kama Loka is our planet, the world of desires. Ananta was born on our planet as Patanjali.
Some people think Patanjali was not a man, but an aphorism or symbol. I personally think he was a man, a real man; but his life and teachings are written in a symbolic way. All Masters love teaching with symbols, parables and even with myths. So their teachings are understood only for the chosen ones.
THE FIRST REAL DISCIPLE OF PATANJALI:
That screen is illusion (Maya). Nobody can see a real Master while he/she is trapped into Maya. When a regular person see a Master he does not see the Master, he sees his body. The body is not the Master; the mind is not the Master. The Master is Atman, he is the inner Master. Whoever wants to see Atman most become ashes, it is fire. In other words, first you most develop your own energies (fire) before you can reach Atman.
The action of trying to see the Master after he said not to do it represents a basic principle in yoga: Obedience. Disciples most be obedient to their Master; otherwise he would not trust the disciple and therefore he would not teach his wisdom. The mind is a traitor, it tells you not to pay attention to the Master, it brings doubt and confusion and finally disobedience.
Whoever wants the teachings of the real Master (Atman) most control the energies and the mind.
The survivor is the chosen one. The action of not hearing is just a symbol that he did not let his mind to disobey. So, he became the real disciple because he did not follow his doubts.
The one who brings the teachings looks like a normal person full of defects. Whoever looks for perfection most learn to accept imperfection. Do not ask for perfection because you are not perfect.
There is a tale about a man who was looking for the perfect Master. He always found imperfections on the Masters he met; so he was going away looking for a perfect one. It is said that one day he found a Master so full of grace on the way he was teaching. He was really surprised, so he was to tell him how long he had being looking for a perfect Master. Then he asked him: <<Are you a perfect Master?>> The answer was: <<Yes, I am, but you cannot be my disciple>> Very confused he asked for the reason. He received this answer: <<Since I am a perfect master I want only perfect students and you are not>>
I bet he received the best lesson of his life.
If you are really willing to find the real Master then you most go beyond the look and imperfections of your teacher. More important, the Master is Atman.
THE YOGA SUTRAS:
Samadhi Pada => Becoming one with Atman (51 Sutras)
Sadhana Pada => Inmersion into Atman (55 sutras)
Vibhuti Pada => Superior capabilities (56 sutras)
Kaivalya Pada => total freedom (34 sutras)