The final boss of Zul'Gurub
Mind Control: Hakkar will randomly mind control people and those MC'ed should be sheeped and then dispel sheep when the MC is gone.
Life Drain: Every 20 seconds hakkar will do a life drain attack that freezes everyone for around 8 seconds while he drains life. It heals him for around 15% HP.
AoE Debuff: Hakkar has a particularly nasty AoE debuff so only tanks should be in range to get it. If poisoned this can deal around 10% of hakkars life.
To fight hakkar you will have to use his life drain against him. There are 2 sons of hakkar which spawn down the right side and the left side of the wooden platform infront of hakkar. Pull them on-top of the raid and kill them thus poisoning the entire raid.
Hakkar will do his life drain but will actually damage himself because of the poison. During the time in-between life drains you should have ranged DPS beating on hakkar but no melee DPS.
All you have to do is repeat the poisoning/life drain and you will kill Hakkar. This is a rather long fight so you will want to conserve mana.