Brahmanarupa Mahakala & Mahasiddha Confusions
Brahmanarupa Mahakala is none other than Chaturmukha Mahakala the special protector of the Guhyasamaja Tantra. In his wrathful appearance he is black in colour with four faces and four hands, surrounded by four dakinis. In the Sakya School it is inappropriate to show the wrathful four-faced form to anyone who has not received the initiation. For this reason the iconographic tradition arose for painting Chaturmukha Mahakala in the form of the Brahman servant.
It is easy to understand why Brahmanarupa has been mistaken for an Indian mahasiddha appearing as he does in a siddha-like depiction. The unique features that he has that are not found with other mahasiddhas are the circle of flame surrounding the body - this is a key feature, followed by the [1] human shinbone horn, [2] sword, [3] golden vase, [4] skull prayer-beads and [5] a skullcup. This combination of attributes is only found with Brahmanarupa.