The temple is unconventional in many respects. Although outwardly it appears to be a typical Drukpa Kagyu temple (the prevailing Buddhist sect in Bhutan), it was probably founded in ancient times as a place of worship for adherents of Bon (or Bonpo), a pre-Buddhist religious tradition that flourished across the Tibetan plateau. Writing in "Seeds of Faith," Thinley notes that the temple was established by a certain "Dewa" who possed the title Zhabdrung and came to Bhutan from the Ralayung monastery in Tibet. Thinley does not give a precise date but hints that the lama might have visited Bhutan before the inception of the Tibetan Rabjyung calendar system, which would place an upper limit on his arrival to the year 1027, roughly a thousand years ago.

The historian Samten G. Karmay provides a later date in tangential references to Kumbu in a longer paper about Dorje Lingpa (1346–1405), one of Bhutan's five famous "treasure revealers" (tertöns). Karmay notes that when Dorje Lingpa was in Bhutan (he was a Tibetan by birth), he stayed for a time at Kumbu temple. In that same paper, Karmay notes that the 69th Je Khenpo, the head of the Drukpa Kagyu order in Bhutan, wrote a short section on Kumbu in 1972. He remarked that "Zhabdrung Tshanden Dewa" came to Bhutan from Yungdrung Ling monastery (in Tibet) and founded two temples in Bhutan: Kumbu and Sewagang. Curiously, he also notes that:

"To this day, performing of the atonement rite according to the Bon tradition and the propitiation rite to Sri Gyalmo have continued [at these establishments]" (Karmay, p. 12).

The Je Khenpo's words suggest that Bon rites were still in practice as late as the 1970s, which is significant; this will be discussed later on this page. As for Tshanden Dewa, the same Dewa mentioned by Thinley, the Je Khenpo's date suggests that Kumbu was founded only in the 19th century—as the Yungdrung Ling monastery was built no earlier than 1834. While this makes sense concerning the use of Dewa's title, Zhabdrung, which only came into parlance in Bhutan from the 17th century onward, it is a relatively late date for the introduction of Bon into Bhutan. Karmay suggests that the discrepancy can be resolved by treating "Tshanden Dewa" as a corruption of "Tshanden Dulwa," a 13th-century individual also known as Dru Dulwa Gyaltshen (1239-1293). Supporting this, he notes that Dorje Lingpa himself described Kumbu as "the seat of Lama Rinpoche Dulwa" (Tshendhen Dewa). Therefore, he believes that Kumbu Lhakhang likely dates to the 13th century.

A third, intermediate date is suggested by Kelzang Tashi in his Ph.D. dissertation, in which he focuses on the use of the "Zhabdrung" title. He suggests an upper limit of the 17th century as to the age of the temple, as the term Zhabdrung would not have been used before that period. It only came into widespread use from the early 17th century onward, following its adoption by Ngawang Namgyal (1594-1651), the founder of the modern Bhutanese state. He also notes that a damaged chorten below the temple, which purportedly holds the ashes of one of Dewa's disciples, is not of 13th-century origin. However, Kelzang Tashi is strangely silent on the question of why, then, Dorje Lingpa references a certain Tshanden Dewa some hundreds of years before his birth, if he was, in fact, a 17th-century individual.

Regardless of the actual date of the temple's founding, it seems likely that the current structure probably dates from the 17th century or later, as it is rare to find standing wooden monuments dating from pre-unification Bhutan.

Source: www.orientalarchitecture.com