There are several opinions pertaining to the origin of this Bodhisattva. The Mahayana tradition believes that he is the spiritual emanation of Akshobhya, one of the Five Transcendent Buddhas and the head of the vajra family. It is also said that in the Buddhist pantheon he seems to be an adaptation of Shakra or Indra ( the god of rain) of Hindu mythology. From early times Buddhist myths and legends associate Shakra (Indra) with many important events in the life of the Buddha Shakyamuni, for instance, his birth, his renunciation, his descent from the Trayastrimsa heaven etc. In early Buddhist art this association has been prominently displayed; the vajra or thunderbolt is the characteristic ayudha of Shakra (Indra) and this personage in Buddhist context came to be known as Vajrapani, a name also associated with Shakra or Indra. In the course of time he was given a place in the Buddhist pantheon and in the Vajrayana phase he came to occupy a fairly important position among the Buddhist divinities.
The Chinese traveler, Huan Tsang mentions that when the nagas (Serpent gods) appeared before Buddha to hear his teachings, Vajrapani was charged by the Buddha to guard them from the attacks of their mortal enemies, the garudas, and that, in order to deceive and combat the garudas, Vajrapani assumed a form with a head, wings and claws like the garudas themselves. Moreover, there are many more legends related to him.
Vajrapani has been represented in Buddhist Art in different forms, postures and gestures. Here he has been shown in a dark blue complexion and standing in the posture of pratyalidha on a lotus base encircled by seven single lotus petals at the front. His left foot is slightly raised up. He has two hands, the right hand is upraised brandishing a vajra, while the left one holds a vajra-pasha (noose).
His expression is ferocious. He is wearing a five-skull crown and his hair is upswept. The three eyes are open and staring. The mouth is open with an upraised tongue. The moustache has been designed on the sides of the mouth. His eyebrows are like small flames and his beard is made of hook-like shapes. He is wearing many ornaments on his body - necklaces, earrings, armlets, bracelets and anklets. A snake hangs from the neck and shoulders like a scarf. Moreover, he is also wearing a flowing scarf and a tiger-skin skirt.
This description by Dr. Shailendra Kumar Verma, Ph.D. His doctorate thesis being on the "Emergence and Evolution of the Buddha Image (from its inception to 8th century A.D)."