Asuras are nature spirits who oppose the gods (aka demons) in Hindu mythology. They have also appeared in Dungeons & Dragons and in Pathfinder, although in both cases they are very, very different creatures.
In Dungeons & Dragons, asuras are actually a kind of angel of Chaotic Good. First appearing in the Monstrous Compendium Appendix for Al-Qadim, they are described as messengers and heralds of the gods. They appear as marble-white-skinned humanoids with birdlike talons for feet, fingers tipped with ruby-colored claws, fiery eyes, red, golden or copper-colored hair, and wings of brightly burning flame. They are loosely organized into groupings known as Hosts, each of which reports to a single "commander" of superior wisdom and greater potency. All asuras together, calling themselves the Grand Celestial Host, recognize a supreme general called Absalom as their leader - this individual is the most powerful of all the asuras, but isn't a fully-fledged god, and nor does he aspire to such a rank.
Occasionally, asuras "lose their way" and choose to take up the calling of good on their own, rather than in service to a god. These are known as Rogue Asuras, and can be somewhat...erratic.
Asuras are known to dislike the aasimon; the two races don't fight it out, they're not fiends after all, but they do regard each other with open contempt.
Asuras are also detailed in the "Warriors of Heaven" and "Planes of Conflict" sourcebooks.
Produced by the various mistakes of gods, Asuras are a bitter and misotheistic array of fiends who absolutely despise their creators and wish to avenge themselves by destroying everything that the gods have made. Which, of course, means essentially everything that exists. To this end, they are a race of contemplative warrior-monks, seeking perfection of body, mind and soul and a proper understanding of the underpinnings of creation so that they better have the skills and knowledge they need to tear reality asunder.
Geryon, one of the Archdevils of Hell, is a former Asura Rana that Asmodeus recruited in his infernal takeover.
As of the release of Bestiary 6, there are six different species of Asura that players can potentially run into.
Adhukaits look like spiky, fiendish humanoids, consisting of two individuals literally interwoven with each other, with limbs penetrating each other's bodies and working through the cavities. Supposedly, the first adhukaits were created when two divine burglars attempted to raid a celestial hall and failed. The occupying god killed the would-be thieves, mashed their corpses together, and then threw the mangled bodies to the ground - unwittingly doing so with such force that they caused earthquakes and tsunamis that killed thousands of people. Many of them worshippers of that idiotic god in the first place. Adhukaits are extremely mobile melee-focused combatants, and extra-tough if you try to use mental attacks against them.
Aghasuras are a fiendish serpentfolk race, looking like giant rattlesnakes with humanoid arms and horns on their heads. They even enjoy wielding scimitars, like the iconic depiction of the yuan-ti abomination. These gargantuan fiends - 30 feet long and weighing 7 tons, on average - are said to have once been the favored pets of a goddess, who ungratefully used the gift of free will she gave them to infiltrate her greatest temple and massacre her most favored priests. For no good reason, mind you.
Asurendas appear as six-armed, horned humanoids, always with multiple eyes and/or heads and typically wearing glowing golden armor and surrounded by floating weapons. These are the mightiest of the Asuras, second only to the Ranas in power, and exist as unholy sages and mystics who seek to unlock cosmic secrets to fulfil the Asura goals of death, sacrilege and shaping. Some Asurendas even have the power to use the souls of mortals they devour as the raw materials to create Tripurasura.
Tripurasuras are the Asura equivalent of imps, tiny humanoids with glowing eyes and multiple horns, created to serve as temptors or as the raw material to be shaped into more powerful forms of Asura.
Upasundas are six-armed, three-faced Asuras who pursue a dark and destructive form of physical perfection - essentially evil fiendish monks. They are said to be the remains of mortals who worshipped a mortal who became a god through his own willpower, but couldn't achieve the same feat themselves, which made them easy prey for the corruptive reshaping of an Asurenda.
Vayuphaks are psionic Asuras who appear as blue-skinned humanoids with two pairs of ebony-feathered wings at their waists. These fiends serve the Asura cause by guarding desecrated holy sites and defiled temples, fighting off any who would seek to reconsecrate the once-holy ground. They are rumored to stem from a divine guardian, who was charged with protecting a sacred treasure that signified a deity's favor. After seeing how many of its own worshippers killed each other to try and take the treasure, that god cursed the artifact to bring madness to whoever possessed it. Unfortunately, the curse drove the guardian insane as well, with Vayuphaks springing into being from the guardian's own fevered, self-loathing-twisted dreams.
|The inhabitants of the Planes of Planescape|
|Upper Planes:||Aasimon - Angels - Animal Lords - Archons - Asuras - Eladrin - Guardinals - Lillend|
|Middle Planes:||Formians - Githzerai - Inevitables - Marut - Modrons - Rilmani - Slaadi|
|Lower Planes:|| Alu-Fiends - Baatezu - Bladelings - Cambions - Demodands - Erinyes - Hags |
Hordlings - Imps - Kytons - Marilith - Obyrith - Succubi - Tanar'ri - Yugoloth
|Transitive Planes:||Astral Dreadnought - Githyanki|
|Inner Planes:||Azers - Elementals - Genies - Grues - Mephit - Salamanders - Sylphs|
|Sigil:||Dabus - Cranium Rats|
|High-ups:||Archangels - Archdevils - Archfey - Archomentals - Demon Princes|
|The Fiends of Pathfinder|
|Lawful:||Asuras - Devils - Kytons - Rakshasas|
|Neutral:||Daemons - Divs - Sahkils|
|Chaotic:||Demodands - Demons - Qlippoth|
|Lords:|| Ahriman - Archdevils |
Demon Princes - Four Horsemen