The spiritual lineage of Gangteng Truelku dates back to the 9th century, to the time when Guru Rinpoche first brought sacred Vajrayana Buddhism to Tibet, Nepal and Bhutan from India. Guru Rinpoches vast spiritual activities left behind an enduring legacy in these countries that has survived vibrantly through the many ensuing centuries until today. Although he was able to subdue negative forces in order for Vajrayana Buddhism to take hold, Guru Rinpoche also saw obstacles that would hinder the Dharma in coming generations, when the teachings would become confused and separated from their essential instructions. To overcome these difficulties, he blessed the region with hidden treasure texts (terma) to be revealed at the appropriate times to be of maximum benefit for sentient beings in the future. The most profound and subtle of these were the teachings on Atiyoga or Dzogchen. During his lifetime, Guru Rinpoche prophesied the later appearance of tertons (treasure-revealers), as well as the appropriate times and circumstances for their discovery of treasure texts. These esoteric teachings were hidden in the varied landscapes of the Himalaya, among the mountains, cliffs, trees, rivers, lakes and caves, as well as in the very mind-streams of disciples who, as re-born spiritual masters, would be led to discover terma through dreams, visions, and spontaneous realization. Up to the present day, many hundreds of tertons have already revealed thousands of these concealed teachings of Guru Rinpoche. Preeminent among them were the five great Terton Kings, of whom Ogyen Pema Lingpa was the fourth.  The legacy of Ogyen Pema Lingpa began in Tibet with the death of Lacham Pemasel- the daughter of King Thrisong Detsen, who died unexpectedly in her eighth year. Perceiving the kings great sorrow over the death of his only daughter, Guru Rinpoche drew Princess Pemasels life spirit back into her body. When she had regained consciousness, Guru Rinpoche transmitted the secret doctrine of the Khandro Nyingthig, or Heart Drop of the Dakini to her, and empowered her to reveal those teachings in a future lifetime. He also blessed her from his heart and prophesied that in a future life she would be reborn as the Terton King Pema Lingpa, and that she would reveal his hidden teachings related to the cycles of the three heart practices: The Lama Jewel Ocean, The Union of Samantabhadras Intentions, and The Great Compassionate One: The Lamp that Illuminates Darkness. Princess Pemasal revealed the Khandro Nyingthig teachings and taught on them extensively in her next incarnation as Pema Lendreltsel, who later took rebirth as the great master Longchen Rabjampa (Longchenpa, 1308-1363). Pema Lingpa was the direct and sole incarnation of the omniscient Longchenpa. Longchenpa was called the "all knowing lord of the doctrine" because his understanding and explanations of the dharma were so exquisitely vast and profound. He could read and write easily by the age of five. Before the age of twenty, he had completely mastered all the Buddhist sciences of grammar and logic; his understanding of the teachings was beyond compare. When Longchenpa was thirty-two, the dakini Vajravarahi appeared before him during a retreat at Rimochen in Chimpu, and told him that in his present life he would serve a great number of beings through the teachings of Dzogchen, and that in his next life he would emanate in Bumthang as the one called Pema Lingpa in order to serve an even greater number of beings.