KATHA OF SREE PADMANABHASWAMY (Ker)

Once, there was a great Vishnu bhakt, Vilwamangalam Swamiyar. One day, Vishnu appeared before him as a child. The Muni took an instant liking to the child and asked him to stay with him. The child agreed but with a condition.

He said he would vanish if he was disrespected.
One day, as Muni was sleeping, the child put the shaligram (that Muni worshipped) in his mouth. The Muni was angry n scolded him. In an instant, the child disappeared telling him to search for him in Ananthankaadu
@SriramKannan77

The Muni ran after him n reached a wooded spot where he thought he saw the child disappear into a huge Ilappa tree. The tree fell to the ground and transformed into the form of Vishnu with head at Thiruvallam (5 km from East Fort where Sree PadmanabhaSwamy Mandir is located).

The feet were at ‘Trippapur’ (8 km away towards North). In total bliss, he requested Prabhu to condense/shrink himself so he could behold the form. It was he who started the custom of presenting Vishnu with raw mango in coconut shell. This continues even today.
@Maha_periyava_

The then Maharaja of Travancore ordered that a Mandir be constructed over this image. Later,
Marthanda Varma, one of the most noted Travancore kings did a major renovation and introduced the festivals Murajapam (chanting of prayers) and Bhadra Deepam.
@ramapriya1989 @pardhu_leo

The murti of Sri Vishnu has 12008 shaligrams in it, brought from Nepal, from the banks of River Gandhaki. The murti is about 18 feet long and can be viewed through three different doors – head and chest through one door, hands through the 2nd door n feet through the 3rd door.