Ontrul Tenpa'i Wangchuk is regarded at the time of writing (2010) as the greatest living master cum scholar of Dzogchen in Tibet. His lineage is Longchen Nyingthig and he has written a number of commentaries on important texts of the system. His commentaries are very unusual; they show his extraordinary knowledge of the system and, magically, his realization is very easy to connect with while reading them. He is clearly a highly accomplished master.
Patrul Rinpoche wrote a small but especially important commentary to Garab Dorje's original “Three Lines that Strike the Key Points” Teaching called Feature of the Expert Glorious King. It is the most-used commentary these days on Thorough Cut within the Longchen Nyingthig lineage but needs explanation. There are a number of commentaries to it but they also tend to be short because they are intended as supports for oral instruction. This text is a commentary to Dza Patrul's text but is unusual in being very long and detailed. It explains every single word of the text step by step so that there can be no doubt over the meaning of the words in Dza Patrul's text. It is hard to emphasize how rare it is to be able to find an explanation as detailed and also as clear as this. In Lama Tony's mind, this is the very best commentary on the Three Lines teaching available. This is the first of Ontrul Tenpa'i Wangchuk's commentaries that we have translated though more are on the way.
For those who are practising Thorough Cut and also those interested in Longchen Nyingthig, these books naturally form a set: Dza Patrul's Feature of the Expert Glorious King text, Dodrupchen III's explanation About the Three Lines, and this explanation by Tenpa'i Wangchuk. Collectively, they give an excellent coverage of the Three Lines teaching. Also, the teaching by Dudjom Rinpoche called Alchemy of Accomplishmentforms an excellent support for them. All of these texts are available just above.