The Rai are one of Nepal

Nepal

Nepal , officially the Federal Democratic Republic of Nepal, is a landlocked sovereign state located in South Asia. It is located in the Himalayas and bordered to the north by the People's Republic of China, and to the south, east, and west by the Republic of India...

's most ancient indigenous ethnolinguistic groups. They were Raya meaning king. Once someone was recognized as a ruler then Hindus awarded the title Raja, Rai, Raya, Malla etc. When the king Pritivi Narayan Shah couldn't defeat Kirant

Kirant

Kirat or Kirati are indigenous ethnic groups of the Himalayas extending eastward from Nepal into India, Burma and beyond. They migrated to their present locations via Assam, Burma, Tibet and Yunnan in ancient times...

 king , he somehow took them in cofidence that the land is theirs forever and gave them the title Rai in around B.S. 1832 .