Sikkim was inhabited in pre-historic times by three tribes namely Naong, Chang and the Mon. The Lepcha who entered Sikkim sometimes later absorbed them completely. The origin of Lepchas is shrouded in mistery but it seems that they belonged to the clan of the Nagas of the Mikir, Garo and Khasia hills which lie to the south of the Bramaputra valley. Some believe they came from somewhere on the borders of Tibet and Burma. According to their own tradition they came to Sikkim from the east in company with Jindaxs, who went to Nepal and shared their tradition. The Lepchas were a very peace loving people, deeply religious and shy, which characteristics they still have retained. They were in fact the children of nature, and worshipped nature or spirits of nature. These Lepcha lived quite close to the nature by way of leading sustenance. Some of them practiced shifting cultivation and raised grains like maize and millets. They led a tribal life at the beck and call of their tribal leader.

The credit of organizing them into some sort of a society goes to a person called Tur ve pa no. He was eventually elected leader of king called "Punu" sometimes in A. D. 1400. He was killed in a battle and was succeeded by three Kings - Tur Song Pa No, Tur Aeng Pa No and Tur Alu Pa No. The monarchy came to an end with the death of the last king. The Lepchas now resorted to the practice of electing a leader whose advice and counsel was sought on crucial matters and followed. The Tibetan migration in early 17th century led the Rongs to shift their habitats so as to avoid conflict. Meanwhile the struggle and conflicts among the followers of the "Yellow hats" and the "Red hats" in Tibet forced the latter to seek refuge in Sikkim, where they attained the status of aristocracy. Being aggressive they occupied lands, which was not registered by the docile Lepchas. These Tibetan migrants (the Bhutias as they came to be known) who were followers of the sect of 'Red Hats' now tried to convert these Sikkimese "Worshippers of nature" to Buddhism. They succeeded to some extent, though the Lepchas tried to keep themselves aloof as far as possible. In order to avoid any possible opposition from the Lepchas, these immigrants now chose one venerable person Phuntsok Namgyal as the temporal and spiritual leader of Sikkim, whose ancestry they traced from a legendary prince, who founded the Kingdom of Minvang in eastern Tibet in 9th century A.D. This dynasty ruled in the Chumbi and Teesta valley for a long time.

Somewhere in the Thirteenth century a prince named Guru Tashi of Minyang dynasty in Tibet had a divine vision that he should go south to seek his fortune in "Denzong- the valley of rice". As directed by the divine vision he along with his family, which included five sons, headed in the southern direction. The family during their wandering came across the Sakya Kingdom in which a monastery was being built at that time. The workers had not been successful in erecting pillars for the monastery. The elder son of Guru Tashi raised the pillar single handedly and thereby came to be known as "Kheye Bumsa" meaning the superior of ten thousand heroes.

The Sakya King offered his daughter in marriage to Khye Bumsa. Guru Tashi subsequently died and Khye Bumsa settled in Chumbi Valley and it was here that he established contacts with the Lepcha Chieftain Thekong Tek in Gangtok. Khye Bumsa being issueless went to Sikkim in the 13th century to seek the blessing of Thekong Tek who was also a religious leader. Khye Bumsa was not only blessed with three sons by the Rong chief but he also prophesied that his successors would be the rulers of Sikkim. Out of gratitude Khye Bumsa visited Thekong Tek a number of times. In due course of times the relationship ultimately culminated in a treaty of brotherhood between the two Chieftains at a place called Kabi Longtsok. This treaty brought about new ties of brotherhood between the Lepchas and the Bhutias.

Mipon Rab the third son of Khye Bumsa assumed the Chief-Ship after the death of his father. He had sons and the four principal clans of Sikkim are said to have sprung from these four sons. The fourth son Guru Tashi succeeded Mipon Rab and shifted to Gangtok. On the other hand after the death of Thekong Tek the Lepchas broke into minor clans. They also gradually turned to Guru Tashi for protection and leadership. Guru Tashi appointed a Lepcha, Sambre as his chief adviser and lieutenant. Guru Tashi's rule marked the absorption of the foreign ruling house into the native soil and also paved a way for a regular monarchy. This way Guru Tashi became the first ruler of Sikkim and was crowned as such. He was followed by Jowo Nagpo, Jowo Apha and Guru Tenzing who pursued the policy creating progressively amicable relation with Lepchas.