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.