Asura, in Vedic religion, were known to be simply gods of moral/social phenomenon who regularly competed with the Devas, who were gods of natural phenomenon. In Hinduism, they are fanatical, demon-like entities associated with carnal and materialistic pleasures, and often thirsted for violence, opposed to the more peace-inclined Devas.
In terms of power, Asuras rank equal to the other deities, and some have levels of power that rival even the most powerful. Some individuals have forced all Hindu-deities to retreat and were defeated only by exploiting their own weaknesses, main one being pride.
In Buddhism, they are the lowest rank of deities who were sometimes considered sinful and materialistic, but most often considered to have become addicted to passions, especially wrath, pride, boasting, and bellicosity. Asura are obsessed with force and violence, always looking for an excuse to get into a fight, angry with everyone and unable to maintain calm or solve problems peacefully.
In Japanese Buddhism, they are demigods, or semi-blessed beings. Powerful protectors of Buddhism, yet fierce and quarrelsome, they are partly good and partly evil, like humans. Their realm is believed to be a world of strife said to be located on the ocean floor. Some say Ashura was an Indian royal who converted to Buddhism. The leaders of the Asuras were called Asurinda or Asurendra ("Asura Lord"). The principal leaders are Vemacritin (also called Vepacitti), Rahu (also called Veroca, Verocana, or Virocana), and Paharada.