Siddhars (Tamil: சித்தர்) are saints in India

Siddhars (Tamil: சித்தர்) are saints in India, mostly of the Saivaite denomination in Tamil Nadu, who professed and practised an unorthodox type of Sadhana, or spiritual practice, to attain liberation. Yogic powers called Siddhis are acquired by constant practice of certain yogic disciplines.
Those who acquire these Siddhis are called Siddhas.^[1] These sidhars can be compared to Mystics of the western civilization. Siddhars are people who are believed to control and transcend the barriers of time and space by meditation (Yoga), after the use of substances called Rasayanas that transform the body to make it potentially deathless, and a particular breathing-practice, a type of Pranayama. Through their practices they are believed to have reached stages of insight which enabled them to tune into the powers hidden in various material substances and practices, useful for suffering and ignorant mankind. Typically Siddhars were saints, doctors, alchemists and mysticists all at once. They wrote their findings, in the form of poems in Tamil language, on palm leaves which are collected and stored in what are known today as Palm leaf manuscript, today still owned by private families in Tamil Nadu and handed down through the generations, as well as public institutions such as Universities all over the world (India, Germany, Great Britain, U.S.A.).^[2]
In this way Siddhars developed, among other branches of a vast knowledge-system, what is now known as Siddha medicine, practised mainly in Tamil Nadu as Traditional native medicine. A rustic form of healing that is similar to Siddha medicine has since been practised by experienced elderly in the villages of Tamil Nadu. (This has been misunderstood as Paatti Vaitthiyam, Naattu marunthu and Mooligai marutthuvam. While paati vaitthiyam or naatu marunthu is traditional Tamil medicine and mooligai marutthuvam is ayurvedic medicine.) They are also founders of Varmam - a martial art for self-defence and medical treatment at the same time. Varmam are specific points located in the human body which when pressed in different ways can give various results, such as disabling an attacker in self-defence, or balancing a physical condition as an easy first-aid medical treatment.
Tamil Siddhars were the first to develop pulse-reading ("naadi paarththal" in Tamil) to identify the origin of diseases. This method was later copied and used in ayurvedha.^[3]
Siddhars have also written many religious poems. It is believed that most of them have lived for ages, in a mystic mountain called Sathuragiri, near Thanipparai village in Tamil Nadu.
One of the best-known Siddhars was Agasthyar or Agasthya, who is believed to be the founding father of Siddha culture.
Abithana Chintamani states Siddhars are either of the 9 or 18 persons enlisted, but sage Agastyar states that there are many who precede these and follow 9 or 18 persons. Many of the great Siddhars are regarded to have powers magical and spiritual.