From The Upanishads (1896)

Patañjali was a sage in India, thought to be the author of a number of Sanskrit works. The greatest of these are the Yoga Sutras, a classical yoga text. There is doubt as to whether the sage Patañjali is the author of all the works attributed to him as there are a number of known historical authors of the same name. A great deal of scholarship has been devoted over the last century to the issue of the historicity or identity of this author or these authors.[1]
Amongst the more important authors called Patañjali are:[2][3][4]
. The author of the Mahabha¿ya, an ancient treatise on Sanskrit grammar and linguistics, based on the A¿¿adhyayi of Pa¿ini. This Patañjali's life is dated to mid 2nd century BCE by both Western and Indian scholars.[5][6][7] This text was titled as a bhasya or "commentary" on Katyayana-Pa¿ini's work by Patanjali, but is so revered in the Indian traditions that it is widely known simply as Maha-bhasya or "Great commentary". So vigorous, well reasoned and vast is his text, that this Patanjali has been the authority as the last grammarian of classical Sanskrit for 2,000 years, with Pa¿ini and Katyayana preceding him. Their ideas on structure, grammar and philosophy of language have also influenced scholars of other Indian religions such as Buddhism and Jainism.[8][9]
. The compiler of the Yoga sutras, a text on Yoga theory and practice,[10] and a notable scholar of Samkhya school of Hindu philosophy.[11][12] He is variously estimated to have lived between 2nd century BCE to 4th century CE, with more scholars accepting dates between 2nd and 4th century CE.[13][10][14] The Yogasutras is one of the most important texts in the Indian tradition and the foundation of classical Yoga.[15] It is the Indian Yoga text that was most translated in its medieval era into forty Indian languages.[16]
. The author of a medical text called Patanjalatantra. He is cited and this text is quoted in many medieval health sciences-related texts, and Patanjali is called a medical authority in a number of Sanskrit texts such as Yogaratnakara, Yogaratnasamuccaya and Padarthavijnana.[17] There is a fourth Hindu scholar also named Patanjali, who likely lived in 8th-century CE and wrote a commentary on Charaka Samhita and this text is called Carakavarttika.[18] According to some modern era Indian scholars such as P.V. Sharma, the two medical scholars named Patanjali may be the same person, but completely different person from the Patanjali who wrote the Sanskrit grammar classic Mahabhasya.[18]
. Patanjali is one of the 18 siddhars in the Tamil siddha (Shaiva) tradition.