There exist two authentic historical lineages for the transmission of the Dzogchen teachings into Tibet. One from India, and the other from Zhang-zhung.
Indian Buddhism came to Central Tibet in the 7th and 8th centuries and was firmly established at the royal court in the mid 8th century with the erection of the first Buddhist monastery at Samye, founded 779. This occurred during the reign of the great Tibetan Buddhist king Trisong Detsän (754-797), who invited the monk-scholar Shantarakshita to his country in order to ordain the first native-born Tibetan monks, thereby introducing the Vinaya and the Buddhist scholasticism of the Sutra system with its Madhyamaka philosophy. The king also invited from Nepal the great Tantric Buddhist master, Guru Padmasambhava, originally from the country of Uddiyana in Central Asia, in order to subdue in magical combat the local gods and demons who opposed this introduction of the Buddhist religion into Tibet. Indian Buddhism, in both its Sutric and its Tantric forms, became the official religion at the court in Lhasa and thereafter generous government subsidies were extended to both the monks and the temples during the eighth and ninth centuries.
The followers of this system of practice deriving from the 8th and 9th centuries came to to be known as the Nyingmapas, “the ancient ones.” This Nyingmapa tradition was preserved among lineages of married Lamas known as Ngakpas, or Tantrikas, who could claim direct descent from the teachings of Padmasambhava and, indeed, the Ngakpa style of practice continues to thrive in Tibet in many areas even today, in parallel to the monastic system.
Thus the Dzogchen teachings preserved in the Nyingmapa school, which were brought from India to Tibet in the 8th century CE by Guru Padmasambhava, Vimalamitra and Vairochana the Tibetan translator, but which are said to have originated with the master Garab Dorje in the country of Uddiyana to the northwest of India.
The Zhang Zhang Lineage is found in the Bönpo school. A practitioner of Bön is known as a Bönpo. Bön centered in the country of Zhang-zhung located in what is now Western and Northern Tibet. Before the 7th century Zhang-zhung was an independent country with its own language, culture, and religion before it was conquered in the 8th century by the Central Tibetans and incorporated in their expanding empire. This centuries old Zhang-zhung culture had close links with Central Asia, or Tazik, and with the Silk Route that ran to the north of Tibet.
Most of these original Bönpo Dzogchen texts are Termas. Having been rediscovered in the 10th and 11th centuries, but there is at least one collection of texts, the Zhang-zhung Nyän-gyud, “the oral transmission from the country of Zhang-zhung,” which represent “kama”, or a continuous uninterrupted tradition of teaching passing down from master to disciple. These teachings are said to derive historically from the master Tapihritsa, regarded by the Bönpos as a Nirmanakaya manifestation, who is also said to have realized the rainbow body of light. In turn, these were transmitted to his disciple Gyerpung Nangzher Lödpo, a Tantric Yogi and Mahasiddha who lived in the country of Zhang-zhung in Northwestern Tibet. He was a contemporary of the Tibetan king Trisong Detsän (754-797), whose armies in the 8th century CE completed the conquest of the once independent kingdom of Zhang-zhung in Northern and Western and brought about its absorption into the expanding Tibetan empire.