Vajrapani is Bodhisattva who appears in a primitive form in the Pāli Canon as a yakkha (sansk. yaksha) a kind of daemonic or chthonic spirit. His name means "Thunderbolt in Hand". In the Vajrapani he becomes a central figure, where he frequently also goes by the name Guhyapati (Lord of Secrets).
The form depicted here is a wrathful form — his body swollen with the energy of liberation is surrounded by a wreath of flames. He shouts his bija mantra; and draws his hand back to hurl the vajra at you in order to break through your obscuration.
Vajrapani belongs to the Vajra Family which is headed by Akshobhya.
If a person has constant fear, if he/she quickly loses energy or has provocation from negative beings, he/she must follow the practice of Vajrapani, reciting the mantra 108 times each day.