Who were the Nayanars and Alvars? …

The Nayanars were a group of 63 saints (also saint poets) in the 6th to 8th century who were devoted to the Hindu god Shiva in Tamil Nadu. They, along with the Alwars, their contemporaries who were devoted to Vishnu, influenced the Bhakti movement in Tamil.The names of the Nayanars were first compiled by Sundarar. The list was expanded by Nambiyandar Nambi during his compilation of material by the poets for the Tirumuraicollection, and would include Sundarar himself and Sundarar's parents.

The alvars, 

were Tamil poet-saints of South India who espoused bhakti (devotion) to the Hindu Supreme god Vishnu or his avatar Krishna in their songs of longing, ecstasy and service. They are venerated especially in Vaishnavism, which regards Vishnu or Krishna as the Supreme Being.

Many modern academics place the Alvars date between 5th century to 10th century CE. Orthodoxy posits the number of alvars as ten, though there are other references that include Andal and Madhurakavi Alvar, making the number twelve. Andal is the only female saint-poet in the 12 Alvars. Together with the contemporary sixty three Shaiva Nayanars, they are among the most important saints from Tamil Nadu.