Sri Singha (Sanskrit: Śrī Siṃha, Tibetan: ཤྲི་སིང་ཧ, Wylie: shri sing ha) was the teacher of Padmasambhava, Vimalamitra, and Vairotsana. He was a principal student and dharma-son of Mañjuśrīmitra in the Dzogchen lineage, and is credited by the Nyingma school with introducing Dzogchen to Tibet. According to the Nyingmapa tradition of Tibetan Buddhism, the Dzogchen masters Manjushrimitra and Shrisimha were already active in the Tantric milieu in India independently. However, Manjushrimitra, a learned scholar of Brahman origin, was evidently an adherent of the Yogachara school before his becoming a disciple of the mysterious Prahevajra or Garab Dorje (dga'-rab rdo-rje) from the country of Uddiyana (Eastern Afghanistan). It should also be recalled that his disciple Shrisimha was said to have born and resided for some time in China (more likely Chinese Central Asia, or, more precisely, Burma, as Chogyal Namkhai Norbu told in a talk he had June 15, 2010) before coming to India. And that the latter's disciple Vimalamitra visited China (or Central Asia) before and after he came to Tibet and transmitted the Dzogchen teachings to his disciples at Samye Monastery. Source: Wikipedia (en)