vajradhara (lit. "holder of the vajra") is the family name given to the class of wrathful beings converted by mahavairocana-shakyamuni buddha. they appear en masse in the yoga tantras, most notably the mahavairocana sutra and the manjushri nama samgiti. the leading vajradhara is vajrapani, also named by the buddha as the supreme primordial buddha (aadhibuddha), for reasons which are esoteric and astounding. vajradhara is also simply another name for vajrapani.
Vajradhara is the primordial Buddha, the embodiment of all the Buddhas of the three time periods, and the essence of the three kayas or bodies of the Buddha.
The Drukpa lineage traces the origin of its transmission to Vajradhara as he is truly the manifestation of the supreme essence of Buddhahood.
With his right hand holding the dorje (symbolizing "method"), his left hand holding the bell (symbolizing wisdom), and the two crossed over his chest, Vajradhara is the ultimate representation of non-duality and emptiness, which is indeed the "Mahamudra", the Great Union - the ultimate realization sought by all practitioners of the Drukpa lineage.