Wikipedia
The Siddhar (Tamil: Cittar from Tamil cittu meaning knowledge, singular Citta, from Sanskrit siddha) are saints in India, mostly Shaiva, in Tamil Nadu, who professed and practised an unorthodox type of sādhanā (spiritual practices) to attain liberation. A siddha obtains yogic powers called siddhi by constant practice of certain yogic disciplines and tapasya. The siddhars can be compared to mystics in Western culture.
Historically, Siddhar also refers to the people who were early age wandering adepts that dominated ancient Tamil teaching and philosophy. Siddhas of tamil region is an exception,as they support idolatory like siddhar Bhogar worshipped lord murugan IDOL in the form of DHANDAYUTHAPANI idol at palani hills,Tamilnadu. They were knowledgeable in science, technology, astronomy, literature, fine arts, music, drama, dance, and provided solutions to common people in their illness and advice for their future. Some of their ideologies are considered to have originated during the First Sangam period.