The list of 18 Siddhas seems to be a matter of continuing debate, while some names, common in northern and western India also evoke debate. These are Valmiki (Tamil name Vaanmegar) and Patanjali: there seems to be a school of thought which believes these were different from their namesakes in the north, while anther school believes to the contrary. But Gorakhnath, prominent in this list, (referred to in Southern treatises as Korrakar) is accepted to be the famous yogi whose imprint is felt even today in Nepal, Bengal and Gujarat. So also Agastiyar's contribution to the yogic philosophy and its healing therapies is recorded as a shared legacy that binds the southern and northern halves of the Indian sub-continent. Dhanwantari, regarded as father of Ayurveda and medicine man for the gods, is also in this list.
Tamil historians also believe Siddhas were part of the Lemuria (in Tamil believed to be Kumari Kandam) – the legendary landmass that linked Australia and Asia, inhabited by highly evolved spiritual people, before it sunk and split gradually. But the history of Siddhas is extremely difficult to track. For one, the language they used was also often obtuse, in yogic parlance called sandhya bhasa or sunya sambhashana(esoteric language), that deliberately hid the meaning of what was meant so the special powers conferred on a Siddha (called Siddhis) did not fall into the hands of unscrupulous people. Again, the reason for the difficulty in spooring Siddhas historically is part of the Siddha legacy itself: the sub-text running through any references to them is the still-common saying "Rishi mulam, nadhi mulam", writes Kandaswamy. Meaning, the source of a saint is as mysterious and untraceable as that of a river.
Though each yoga school may insist that their method is superior to the rest, the common purpose – of god-realisation – is the binding factor in all of them. In that the Siddhas have much in common with other yogic traditions in India. But the emphasis was on using the body, perfecting it as the ideal vessel that carried them to this destination. This vessel had to be perfect, non-decaying, youthful and absolutely strong for that difficult task. That explains the vast therapeutic branches that this type ofyoga spawned, including the anti-aging Kaya Kalpa. This also explains the mythical life-span attributed to the Siddhas, most of them, according to the legends that surround them, lived for thousands of years. And some of them are also revered as Chiranjeevis, those who never died and are still around to help their devotees transcend the turbulent ocean of samskaras (cycle of births and deaths). This includes the legendary Babaji, the guru of many recent masters. The legend that surrounds his `sightings' even today draws yoga devotees from around the world to brave the cold, snow-strapped slopes of Himalayas.