Parameswara

The region where the temple is located was called Vidarbha Desa and ruled by a king named Viroacha. Due to misdeeds in preceding birth had no heir. He prayed in Kailasanathar Temple

http://6kan.blogspot.com/search/label/Kailasanathar

and Shiva, the presiding deity of the temple gave a boon that the Dvarapalas (the gatekeepers) of the Vishnu temple will be born as sons to him. The princes were devoted to Vishnu and conducted yagna for the welfare of the people of their kingdom. Vishnu was pleased with the worship and appeared as Vaikundanatha to the princes.

Three sanctuaries host the image of Vishnu in different postures -

1. seated (ground floor), 
2. lying (first floor; accessible to devotees only on ekadashi days) and 
3. standing (second floor; inaccessible to devotees). 

The logical and complex plan of the temple provided a prototype for the much larger shrines to be constructed all over Tamil Nadu.

The external cloisters, for instance, with their lion pillars, are predecessors of the grand thousand pillared halls of later temples.

https://en.wikipedia.org/wiki/Tiru_Parameswara_Vinnagaram

eswarar

The lingam (an iconic representation of Shiva) got a from forest in the region by asuras (demons)

1. Onan 
2. Kanthan
3. Jalandeeswaran, 

The three shrines in the temple, each dedicated to

1. Onakantheeswarar, 
2. Salantheeswarar and 
3. Jalandeeswarar are 

the respective shrines built by demons.

https://en.wikipedia.org/wiki/Ona_Kantheeswarar_Temple
https://www.youtube.com/results?search_query=Ona+Kantheeswarar