What is "tirumular"

Tirumular (also spelt Thirumoolar etc., originally known as Cuntaranātar) was a Tamil Shaivite mystic and writer, considered one of the sixty-three Nayanars and one of the 18 Siddhars. His main work, the Tirumantiram (also sometimes written Tirumanthiram, Tirumandhiram, etc.), which consists of over 3000 verses, forms a part of the key text of the Tamil Shaiva Siddhanta, the Tirumurai.