The hill area cast of the Kosi river was known as Denzong (valley of rice) to Tibetans. Earlier settlers, the Lepchas, called it Neliang (the country of caverns).
When a Lepcha chief brought his newly wed Limbu wife to his newly constructed bamboo house, she is said to have exclaimed, "Sukhim!" — the new house. This is how the name Sikkim came to be applied to this forested, hilly territory which lies east of Nepal's Limbuan and west of Lho'mon (Bhutan).
Three Bhotia lamas came down to Denzong in search of new land and converts. As they could not resolve their separate claims, in 1641 AD, they invited Phuntso Thondup Namgyal, a local patriarch, to be the chogyal (the one who rules according to the chho, or religion).
The kingship thus acquired was lost by Phuntso Thondup's 12th descendant Palden Thondup Namgyal in 1975, when Sikkim was incorporated into India.