Harbinger of Death
Harbinger is located within the UK UD Temple.
Harbinger is a tough fight. He is surrounded by numerous demons that cast. They stand on their own islands which makes hand to hand virtually impossible. However, magic and range work well on them. They must be killed as soon as they spawn as they do hit hard and can easily wipe a group.
Harbinger is not known to jump around too much (if at all??) so it is best to try and use a tank or DJ/Efreet to agro him. He has an enormous amount of health.
His drops include gems that is worth an enormous amount of gold, black and red robe (best for casters), Water Breathing bracer that includes regen, and the 7/7 Rhammer.