Belial is the final boss of SpellForce: Shadow of the Phoenix.
Hokan Ashir used the powers of all 13 Circle Mages, including himself, to combine his powers with that of Belial, the God of Death. You can still see Hokan's Mask on the creature.
Hokan Ashir is the Circle Mage of Death. In Spellforce - The Order of Dawn, the player must find two halves of a mask, which must be given to Hokan Ashir in Whisper. After that, the player does not see him again. In Spellforce - Breath of Winter, Hokan even helps the player. But in Spellforce - Shadow of the Phoenix, he commands the Shadow Warrior to do his bidding and resurrect the Circle Mages, hoping to become the new god of Death.
Belial is a very though boss, dealing over 300 damage to level 50 casters. To make him vulnerable to your attacks, you have to damage the Circle Mages casting protective spells on him.
He can also summon various creatures through two Demon Gates:
Blade Changers are tough level 36 Blade Minions, which increase in level the longer they can stay alive.
They change appearance, at level 40 they change into Weavers and at level 46 they change into Captains.
Burning Sacrifices are Elementals that move close to the units, deal a lot of damage and then disappear. They have been seen dealing over 600 damage.