Srimathe Ramanujaya Namaha,
The 12 Alvars were considered incarnations of ParaVasudevan’s divine accessories (NithyaAtma’s) imparted on a BhadhAthma. They appeared in material world to spread Bhakti.
Adiyen have not heard in Swami’s upanyasam which BhadhAthma they were in previous birth, as it is immaterial.
Divine Incarnations of ParaVasudevan’s Attributes:
Poygai Alvar: Panchajanya/Shankham (conch)
Bhoothath Alvar: Kaumodaki (mace)
Pey Alvar: Nandaka (sword)
Thirumalisai Alvar: Sudarshana (discus)
Nammalvar: Vishwaksena (Vishnu’s commander)
Madhurakavi Alvar: Garuda (divine eagle/mount)
Kulasekhara Alvar: Kaustubha (gem on Vishnu’s chest)
Periyalvar: Garuda (sometimes cited as Ratha/chariot)
Andal: Bhoomi Devi (Goddess Earth)
Thondaradippodi Alvar: Vaijayanti (garland)
Thiruppaan Alvar: Srivatsam (mark on Vishnu’s chest)
Thirumangai Alvar: Saranga (bow)
Adiyen recommend to listen to Swami’s upansyasam on “Alwargal Vaibhavam”
Adiyen (ElayaAlwar) Srinivasa (DhaddayacharyAr) Dasan