Algalon the Observer had the power not strenght , the power to make the decision to wipe the planet of all life if there was too much corruption . luckily the players together with Bran could stop him . Deathwing was the Earthwarder and could destroy the planet if he wanted to but it would be no use broken . Kiljaden and archimonde are the 2 ndish in command of the burning legion and we didnt kill kiljaden just pushid him back into his portal . But fore pure brute force power , the old gods are the strongest . In ulduar we fight just the tip of the iceburg . the old gods can not die because they are burried and rooted so deep into Azeroth that the wound left from removing them will kill the slumbering titan . The old gods can corrupt any mind as long as that mind is desperate for more power . this is all of the top of my head but should be mostly accurate so correct me if im wrong .