Vajrayana (the vehicle of the thunderbolt)
It is perhaps clearer for the uninitiated to think of the five Buddhas as the five aspects of Buddha-hood. Known as the Dhyani Buddhas, or Buddhas of meditation, whose cosmic nature is demonstrated by the fact that while one was associated with the centre of things, the others radiated out to the four points of the compass.
Later, with the development of the Vajrayana school, Tantric elements were adopted from Hinduism. These implied the introduction of a feminine principle, in a state of simultaneous polarity and fusion with the masculine one. Accordingly, a system of female deities came to be associated with the five Buddhas. The circular design of the mandala was an attempt to express in graphic terms the essentially abstract relationships between all these symbolic concepts.
This brief description of a few salient points does no more than hint at the enormous complexities of the Vajrayana school, which established itself in Tibet from about the 11th century as a mystical and esoteric religion relying largely on practices and initiations derived from the secret texts of the Tantra.
Historically too, Buddhism in Tibet had to contend with the pantheistic and shamanistic Bon religion, which was characterized by a highly-developed cosmic system and a multiplicity of gods and demons. Buddhism, as it spread made no attempt to suppress this ancient cult altogether, but rather absorbed many of its beliefs and practices.
Thus many of the Bon deities appear in the Buddhist pantheon, where they have the position of Dharmapalas - Guardians of the Law. It is they with their fearful aspect that play such a large part in the annual dance dramas held by each monastery on the days of its own particular festival.