According to the anuttara yoga tradition of the vajrayana, your root guru is the embodiment of all buddhas because the mind of the guru is the dharmakaya, the wisdom of all buddhas. Since the guru is the source of Dharma, the speech of the guru is the embodiment of all Dharma. Whether the guru manifests as a monastic or as a chakravartin, the body of the guru as the foremost member of the sangha is the embodiment of the whole sangha. The qualities of the guru are what manifest as the yidams and other deities, and the activity of the guru is what manifests as dakinis and Dharma protectors. In Karma Chakme's Mountain Dharma your root guru is defined as the teacher who points out the nature of your mind.