Vajrapāṇi is bodhisattva who appears in a primative form in the Pāli Canon as a yakkha (Sanskrit yakṣa) a kind of daemonic or chthonic spirit. His name means "Thunderbolt in Hand". In the Vajrayāna he becomes a central figure, where he frequently also goes by the name Guhyapati (Lord of Secrets). In the Tantric texts he is seen in dialogue with the Cosmic Buddha Mahāvairocana.
The form depicted here is his peaceful manifestation, sitting in 'royal ease' and balancing the vajra in the palm of his hand. He is deep blue in colour. He also has a wrathful form - his body swollen with the energy of liberation is surrounded by a wreath of flames; he shouts his bīja mantra hūṃ and draws his hand back to hurl the vajra at you in order to break through your obscurations. He is frequently depicted trampling on the Hindu god Śiva whom he defeats in a contest of magic in the Sarvatathāgatatattvasaṃgraha Tantra, converting him to Buddhism.
|Siddhaṃ||Tibetan - Uchen|
The astute observer will notice that I have written ṇa in two different ways - compare Vajrapāṇi's name with his mantra. The form used in his name is a simplified version of the formal letter that I have used in the mantra. Several other Siddhaṃ letters have alternative forms.