Trisong Detsen was the son of Me Agtsom, the 38th emperor of Tibet. He ruled from AD 755 until 797 or 804. Trisong Detsen was the second of the Three Dharma Kings of Tibet, playing a pivotal role in the introduction of Buddhism to Tibet and the establishment of the Nyingma or "Ancient" school of Tibetan Buddhism.
The empire Trisong Detsen inherited had declined somewhat from its greatest extent under the first Dharma King, Songtsen Gampo. Disintegration continued when, in 694, Tibet lost control of several cities in Turkestan and, in 703, Nepal broke into rebellion. Meanwhile, Arab forces vied for influence along the western border lands of the Tibetan empire.