The Deva are an ancient people of Sri Lanka.
Dewa (people) Wikipedia
The Deva are an ancient people of Sri Lanka according to the Sanskrit epics. According to the Mahavamsa and Ramayana, they lived among the Naga, Yakkha and Raskha. They ousted their arch enemies the Raskha from Sri Lanka, with the help of Lord Vishnu. They were then subsequently conquered by King Ravana of the Raskha. After the Yakkhas had left to live in the mountains and remote dense forests, they met Gautama Buddha who converted them to Buddhism.
According to the Mahavansa, Gautama Buddha meet the Deva at Mahiyangana. Buddha gave Sumana Saman (a leader of the Deva) a few hairs from his head, which were placed in a golden urn and enshrined in a sapphire stupa. A Buddhist monk called Sarabhu is then said to have deposited Buddha's ashes in this Stupa. This stupa is now called the "Mahiyangana Stupa" and can be found in Anuradhapura Museum.
Sumana Saman was a leader of the Deva who came from the central hills of Sri Lanka. Some Sri Lankan Buddhists worship him as a deity. He is said to be the guardian of Adam's Peak.
During the ascention of the Raksha King Ravana, some Deva people migrated to other places like present North Malabar of Kerala where they followed Buddhism before the advent of Brahminism. Having their own complete social fabric and systems of precedence and worship, they dominated the area, until their power was seriously undermined by Brahmin lead power lobby. However, they still survive in Malabar, and are known as "Thiyya", a localisation of the name "Deyva" equivalent to Deva. The ancestor worship of Thiyyas spring from the fact that they consider themselves as descendents of "Deyva" or God. The ceremonial oracle, who represent the spirit of their ancestors of Lanka, in the temple are known as "Theyyam" origiting from the word "Deyvam" meaning God. However, by the time of arrival of Vijaya to Sri Lanka it had noted a significant presence of Deva clan In which latter got mixed with North Indians, Nagas and Yaksa to create the Modern Sinhalese lineage.