From Diablo Wiki
 Belial in Diablo 3
Belial had once been a protege of Mephisto, honing his powers of deception under the Lord of Hatred's guidance. Eventually, he would turn on his mentor and manipulated Azmodan into leading a revolt against the Prime Evils, though this may have likely been indirectly encouraged by Mephisto himself. With the armies of Azmodan and Belial unified, the Prime Evils were cast out of Hell, though at the expense of a full third of Hell's demons. Azmodan and Belial were left to vie for power over the Burning Hells, a conflict Belial ultimately lost. Years later, much like the Prime Evils, Belial would turn his attention to Sanctuary and corrupting its populace. His influence over the mortal realm mirrors Mephisto's own of twenty years prior, as his power over Caldeum, capital of Kehjistan, was nearly complete until he met an untimely demise at the hands of the nephalem. He later became a part of the Prime Evil, who was defeated, again by the nephalem. He is within the Black Soulstone at this time.
 Boss Fight Guides
http://www.gamersheroes.com/2012/05/17/diablo-3-beating-belial/ - has some background information to know before taking on Belial.
 The Lord of Lies
All greater and lesser evils of the Burning Hells have their own specific title or aspect, and Belial's is the Lord of Lies. Along with Azmodan, Belial helped in a rebellion against the Prime Evils to seize control of Hell. From the Diablo I Manual:
- In their ignorance, the Lesser Evils began to believe that the Three were afraid to continue the war with Heaven. Frustrated by the cessation of the war, Azmodan and Belial saw the situation as their chance to overthrow the Prime Evils and take control of Hell for themselves. The two demon lords made a pact with their minor brethren, assuring them that the wretched plague of humanity would not deter the ultimate victory of the sons of Hell. Azmodan and Belial devised a plan to end the stalemate, achieve victory in the Sin War and ultimately ride the bloody crest of the Great Conflict straight into the very arms of Armageddon. Thus, a great revolution was set into motion as all of Hell went to war against the Three Brothers...
- The Brothers fought with all of the savagery of the Underworld, and to their credit, annihilated a third of Hell’s treacherous legions. In the end, however, they were overcome by the Horned Death led by the traitors Azmodan and Belial. The Prime Evils, weakened and bodiless, were banished to the mortal realm where Azmodan hoped that they would remain trapped forever. Azmodan believed that with the Three set loose upon humanity, the Angels would be forced to turn their focus upon on the mortal plane - thus leaving the Gates of Heaven abandoned and defenseless. Those few demons who still pledged allegiance to the Three Brothers fled the wrath of Azmodan and Belial, escaping to the realm of Man to seek out their lost Masters.
- As the warfires died out upon the battlefields of Hell, Azmodan and Belial began to argue over which of them held the higher authority. The pact that they had made quickly fell to ashes as the two demon lords took up arms against each other. The legions of Hell that remained were polarized behind either warlord, launching themselves into a bloody civil war that has lasted to this day...
 Boss Abilities
The Belial boss encounter is in three phases. Each phase is broken down below.
 Phase 1
Belial does not take part in phase 1, opting instead to call in the troops. He'll summon a large amount of Veiled Sentinels and Veiled Evokers to challenge the player. The sentinels just have a melee attack, the evokers have the magus ability to wiggle around a lot and summon a ring of electricity that damages anything inside of it. They both retain the snakeman ability to vanish and then re-appear.
 Phase 2
After the snakemen prove to be fairly ineffectual, Belial himself drops down into the throne room to battle the player. Snakemen are still spawned later on during this phase, and drop a good amount of health globes. Belial himself has a few abilities in phase 2.
- Fireball - Belial launches three fast-moving fireballs along the ground at medium range. They are green and black, and probably not made of fire, showing that Belial really is a liar.
- Melee Attack - He has a basic melee attack in this phase that hits for low damage.
- Reinforcements - Belial will call in more snakemen to challenge the hero. They drop health globes.
When Belial is at under a quarter health, the final phase begins.
 Phase 3
Phase 3 is when the real fight begins, and Belial gains a lot of new abilities.
- Ground Pound - A ring of green appears on the ground where Belial is about to strike. He'll strike three times, with the last being him pounding the ground with both arms. The first strike is off to the side of the player, allowing for some wiggle room. The last two happen in the same location (where the player is).
- Poison Strike - Belial will put his claws into the ground of the throne room, and green rings will show up all over the arena. After a second or so, the rings explode for poison damage. This continues for 10-20 seconds. It is difficult to dodge them, but it can be done
- Poison Breath - Belial will breathe a poison cloud from one end of the arena to the other. It leaves no lasting effects, as it only deals a small amount of damaged compared to the other goodies he packs.
 Associated Achievements
Belial is in some way involved in the following achievement(s).
| Death from Afar
|10|| Kill one of the following enemies with a thrown weapon.
| A Cut Above
|10|| Cast Spectral Blade as the killing blow on the following enemies.
|Difficulty||Max. Health||Min. Damage||Damage Delta||Run Speed||Level|
- http://www.youtube.com/watch?v=jexsWgaS51E&noredirect=1 - Guide on killing Belial.
- IGN interviews Jay Wilson
- Diablo3.cc Interview with Jay Wilson
- Diablo 3 Belial Walkthrough | Monk Solo Hell Difficulty | The Healthy Gamer
|Monsters of Diablo III Beasts Beasts: Superunique Demons Demons: Superunique Humans Humans: Superunique Undead Undead: Superunique Objects Bosses Boss Mods Monster Info Fanmade|
Bat - Beast - Blood Hawk - Demonic Hellflyer - Electric Eel - Khazra - Lacuni - Lamprey - Quill Fiend - Rockworm - Sand Monster - Sand Shark - Sand Wasp - Scavenger - Spider - Spiderling - Swarm - Withermoth - Wood Wraith -
|Primary Quest Uniques||
Act One Bosses:
Skeleton King -
The Warden -
Strong CC (Limit 1): Knockback -- Nightmarish -- Vortex -- Jailer
|Act One Uniques||Araneae - Web Spit||Leoric - Summon Skeleton, Teleport Strike, Triple Cleave||The Butcher - Smash, Grappling Hook, Spear, Frenzy Charge|
|Act Two Uniques||Maghda - Forcefield, Summoning Ritual, Punish, Moth Dust, Teleport.||Zoltan Kulle - Fiery Boulder, Time Bubble, Ceiling Collapse, Energy Twister,Vanish, Creepy Laugh||Belial - Phase One: Triple Fireball, Summon Vipers. Phase Two: Poison Meteors, Ground Pound, Lightning Strike, Lightning Breath.|
|Act Three Uniques||Ghom - Acid Slime, Sneeze, Gas Cloud, Chomp.||Siegebreaker - Triple Hit, Charge, Leg Stomp, Grab and Throw.||Cydaea - Pain Bolts, Web Trap, Spider Pits.||Azmodan - Bellyflop, Laser Attack, Falling Corpses, Demon Gate, Pool of Destruction, Globe of Annihilation.|
|Act Four Uniques||Rakanoth - Cleave, Teleport Strike, Blade Strike, Volley, Summon Minion.||Izual - Frost Nova, Frozen, Summon Minions.|| Diablo - Phase One: Claw Rip, Charge, Hell Spikes, Shadow Vanish Grab, Curse of Destruction, Ring of Fire, Ground Stomp, Curse of Anguish, Curse of Hatred. |
Phase Two: Shadow Clone. Phase Three: Overdrive, Lightning Breath.
|Characters & NPCs Import. Chars Rumoured Diablo 3 NPCs Diablo 2 NPCs Diablo 1 NPCs Minor A-K Minor L-Z Fanmade|
|Diablo III's Possible NPCs|
|NPCs of Diablo II||
Achilios - Adria - Akara - Albord - Aldric Jitan - Alkor - Anya - Arkaine - Asheara - Assur - Atma - Augustus Malevolyn - Baerna - Banagar - Benjin - Brek - Buyard Cholik - Camylle - Celestia - Cornelius - Darrick Lang - Diomedes - Drognan - Edgewulf - Elora - Elzix - Emilye - Fara - Farnham - Fautzin - Galeona - Garda - Gheed - Gillian - Gorst - Greiz - Griswold - Guthwulf - Hagan - Halbu - Hanos Jeronnan - Hargo - Hays - Hratli - Hrothwulf - Humbart Wessel - Hunfrith - Hyram - Icharion - Jace - Jamella - Jerhyn - Jodas - Juris Khan - Justinian IV - Kabraxis - Kara Nightshadow - Karybdus - Kashya - Kentril Dumon - Kethryes - Korlic - Kreghn - Ku Y'leh
Lam Esen - Larzuk - Linarian - Lysander - Malah - Mat Hu-Ring - Meshif - Mirakodus - Mordecai - Natalya - Nefriti - Nellia - Nihlathak - Nor Tiraj - Norrec Vizharan - Ogden - Ord Rekar - Orlif - Ormus - Oskal - Palashia - Pepin - Qarak - Qual-Kehk - Riordan Nesardo - Sadun Tryst - Salene Nesardo - Sardak - Sarnakyle - Septumos - Simon - Talic - Taramis Volken - Tilgar - Tobio - Toko - Tylwulf - Vischar Orous - Warriv - Wirt - Wulfgar - Xazax - Zagraal - Zayl - Zorea