Tritsuk Detsen, better known by his nickname Ralpachen, was the 40th king of the Yarlung Dynasty of Tibet. He reigned after the death of his father, Sadnalegs, in c. 815, and grew the empire to its largest extent. He was murdered by his younger brother Langdarma in 838. Ralpachen is one of Tibet's three Dharma Kings, and referred to as "son of God" in the ancient Tibetan chronicle Testament of Ba.

The Testament of Ba or the Chronicle of Ba(Tibetan དབའ་བཞེད or སྦ་བཞེད; Wylie transliteration: dba' bzhed or sba bzhed) is a chronicle written in Classical Tibetan of the establishment of Mahayana Buddhism and Vajrayana Buddhism in Tibet, the foundation of the Samye Monastery, and includes notable events and people in Tibet's history and was written during the Tibetan Empire period. From the reigns of kings Songsten Gampo, Trisong Detsen, and to the years beyond Rapalchen's reign, a version of the chronicle, or testament, was recorded by Ba Salnang of the Ba Family, and by other scribes and members of the kings' courts. In 2008, early versions of the text were said to have been discovered in London, where two manuscript fragments possibly dating to the 9th or 10th centuries are held by the British Library.