Lord Onsten is an Erathian Lord appearing in Hopewielder, the first scenario of Revolt of the Beastmasters, which is the seventh part of Heroes Chronicles.
The Ancestors sent Tarnum to free the Mudlanders from Erathian slavery, and he arrived in the lands of Lord Onsten. Lord Onsten was one of the cruelest of the Erathian nobles. The slaves in his mines were chained to their work areas, never allowed to leave. They lived and died on the spot, and the stench of unwashed bodies was nauseating. When saw this, Tarnum realized that the slavery the barbarians had experienced under the Wizard-Kings of Bracaduun was nothing compared to the plight of the Mudlanders.
Tarnum planned to gather a group of local slaves and sneak away with them, gathering an army before he saw any real combat. Unfortunately, Lord Onsten heard about their rebellion, and tried his best to scare the slaves into abandoning their cause. He cut the arms and legs of a gnoll slave and cauterized the wounds, leaving the dying gnoll on the side of the road for Tarnum's army to find. When a group of escaped slaves returned to surrender themselves to Lord Onsten's mercy, he asked them to dig a massive hole in the swamp, and then told them go inside the hole and had his archers shoot them all. The news broke the morale of Tarnum's army, and he realized that he had to kill Lord Onsten to regain their faith.
Lord Onsten proved no match for Tarnum's might, and he was slain. Unfortunately, the news of his death enraged the other nobles. Mad King Gryphonheart killed the messsenger who brought him the news, and then burned down his own stables. Baron Paglon decided to deal with Tarnum's rebels.