Nandi Devar Siddhar:

Nandi Devar is one of the foremost of the 18 yoga siddhas. He has been directly initiated by Lord Shiva himself and some of his contributions include medicine, kaya kalpa & Alchemy. Some of his eminent disciples are Thirumoolar, Patanjali, Dakshinamoorthy, Romarishi & Sattamuni.