Yidam
The second root is the meditational deity or yidam. The iconography of the yidam may be 'peaceful', 'wrathful' (Tibetan tro wa) or 'neither peaceful or wrathful'(Tibetan: shi ma tro), depending on the practitioner's own nature. The yidam represents awakening, so its appearance reflects whatever is required by the practitioner to awaken. The guru guides the student to the yidam appropriate for them, then gives them initiation into the mandala of the yidam. In essence, the mind of the guru and the yidam are one. The yidam is considered to be the root of success in the practice.
Read more about this topic: Three Roots, The Individual 'roots'