Sadam - It's a kind of vayu/air that would surround the fetus and keeps the baby ignorant of its past life or memory about previous births.
SADAGOPAN [ Meaning - sada - A kind of vayu/air, Kopam - anger in tamil ]
By nature, before the baby was born, the sadam entered into the womb of mother to cover the fetus, but being a blessed soul, it got angry on it and drove the air/vayu away and hence the name Sada-kopan or Sadagopan. Other name for Sadagoban or Sadagopan is '
Namalwar'. This was said to be name given by Lord himself.
It is said that the parents of 'Namalwar' were not blessed with a child for so many years. They were pious and were devoted to 'Thirukarunkudi Nambi' [Tirunelveli - Tamilnadu - South India]. When they prayed to the Lord to bless them with a son like HIM, HE himself was said to have born to them. As mentioned before, each Alwar would assume a form of a 'Nithya Soorya', and 'Namalwar' assumes the form of 'VishwakSenar' [Vishwa means world, Senar means Chief of Army of Lord]
As soon as the baby was born, it was said that for nearly 16 years, he was in trance living in a hole in a tree. The significance of the tree is, it is none other than 'Adhi Sesha, the snake bed of the Lord. It has taken the form of a tree and waited for Sadagopan to rest on it. The name of the tree is 'thiru puliya [tamarind] maram [tree in tamil language], Uranga puli [uranga means sleepless puli - tamarind tree]. The next 16 years he had sung 4 'divya prabandams'. They're are 'Thiruvirutham[100], Thiruvasiriyam[7], Peria Thiruvandadhi[87], and Thiruvaimozhi[1102]. It is to be mentioned here about 'Madhurakavi Alwar' who wrote all prabandam on palm leaves and delivered it for the benefit of human society.