The Dark One is a mighty mage of The Circle, who hides his identity under a dark hood, that appears in SpellForce: The Order of Dawn. He is both influential and wealthy, managing to control the blades and the Black Fist.
On the day of the Convocation he was approached by an old man later on shown to be Rohen, clutching an arcane tome containing the secrets of the ritual. The old mage warned the Dark One that the Convocation was a lie and that it would destroy them all.
Arrogantly dismissing him as an old fool, the Dark One flung him across the room, mocking him for thinking that he cared about his 'whimpering'. During their fight an army of Humans did battle with a horde of Orcs outside, until the magic released during the ritual of the convocation released the elements from their bonds.
It was then that Rohen was proven right as the earth split, swallowing many warriors from both armies. As his tower collapsed around him, the Dark One and his foe stood upon pieces of rubble as they plummeted to the ground. Both sighting the Book of the Convocation they flung themselves downward, straining to reach the invaluable tome.
Evidently the old man won. With his armies destroyed and the world in ruin, the Dark One was left embittered and frustrated. He believed he failed not because the Convocation was never meant to succeed, but because he did not fully understand it.
To that end he began to obsessively work towards acquiring the Book of the Convocation, that tome carried by the old man who came to him on the day the world was shattered. Surely he thought, with the knowledge contained within the tome, he could succeed where previously he had failed.
In the years following the convocation, when Rohen was travelling the world creating the Portals to unite the islands that had once been a united continent and forming the Order of Dawn, the Dark One was plotting. He amassed a great fortune and used this to acquire the services of the Black Fist, a vast mercenary army of Orcs. Through unknown means, he also gained command of the Blades, also known as the Iron Ones, constructs of black iron created by the great Necromancer and Circle Mage Hokan Ashir during the Convocation Wars to fight the demon hordes of his rival Uram the Red. Now they blocked the path into the Frost Marches and threatened to swarm south and destroy everything.
Years later, he brought his plan into action, sending the Black Fist out to attack Humans and Elves of Nortander, sowing chaos wherever they went. Meanwhile his blades blocked off all access into Frost Marshes and began swarming into the Wildland Pass. Rohen, seemingly having foreseen these events, had gained the means to summon a particular Rune Warrior. Travelling to Greyfell he summoned the warrior and gave him his own rune, granting him his freedom and sending him east to Greyfell to report to Sartarius and the Order of Dawn, before heading to the Wildland Pass. The Dark One ambushed the Rune Warrior as he traveled, the messenger set to show him the way revealed as a traitor. Frozen in ice, the warriors listened helplessly as it was revealed Rohen was walking into a trap set by this hitherto unknown Circle Mage. Handing the messenger a casket meant for the leader of the black hand, the Dark One casually ordered the Rune Warrior's death. Released from the ice, the warrior easily killed the messenger and hurried to Greyfell with the casket. It was soon revealed that the casket was sealed with magic that could only be broken by another Circle Mage.
Rushing north, through numerous islands ravaged by the Black Fist, the Rune Warrior finally reached the Frost Marshes. Warning Rohen of the danger and delivering the casket, it was revealed that the trap was to be delivered by the Rune Warrior himself. As soon as the box was opened, Rohen and the warrior were frozen in ice and the Dark One appeared, gloating before he killed Rohen.
Upon having killed Rohen he reads on the tome and discovered its content. See this article for further details.
Fight between Rohen and the Dark One during the Convocation
Although being a circle mage strong enough to kill another circle mage instant and wielding the Allfire power the Dark One still keeps a rusty orcish dagger as a weapon which seems vastly inappropriate. It is not mentioned if the dagger has a lore-wise connection but upon reviewing the game stats the dagger was definitely identified as 'Rusty Orcish Dagger'.
As this article shows the specific ways of how the Dark One (also known as Young Rohen) proceeded after the Convocation this article is left standalone to avoid confusion within the Rohen article.