To get to the Abyss, where this boss is located, you need to kill Sif and equip the Covenant of Artorias (you die if you don't have it equipped); you need to have it equipped for the whole battle. This is a special fight, because as time goes on, up to four bosses will join the battle; thus, it is crucial that you quickly kill each one. Each King represents one fourth of the total health on the bottom of the screen. All four have the same move set, so you don't have to worry about different attacks. You can summon Witch Beatrice for this fight; her sign is by the drop off that would put you at the beginning of the ruins. The Four Kings' attacks are pretty basic. There is a sword thrust that's pretty easy to dodge, as well as horizontal swing. There are a couple of other attacks, like one where the King will grab the player and do some damage before releasing. If you see the King huddling up, then try to get away, because it will release a shockwave explosion. If you are far away from the boss, then they will create a homing projectile that follows you for quite a while. As said before, speed is the key to this battle, as you don't want all 4 Kings on the field at once. One of the good strategies for this battle is to bum rush each one and don't worry about blocking. This is very possible with armor that has high poise (Havel's set) and with the Iron Flesh spell. You should only heal when your health dips below 40-50%, as you want to be sure you survive any random chance of heavier than normal damage. Fire damage does more than any other magic damage, so pyromancies and fire-enchanted weapons are good.