The Great King Herne was the leader of Solum, however for some reason, hadn't followed protocol of commiting a ritualistic suicide at the height of his power, to pass his legacy onto his son, Jared. It is this, what seems to be, selfish act that has turned Solum into a wasteland and aligned it with Chaos.
Jen and Scree seek out Herne and although their first encounter warrants a warning that they should leave his Kingdom or be left to the barbaric Malkai, Herne eventually comes round to his senses when Jen and Scree reveal to him a fragment of Jared's horn when he is praying at the Great Temple. The reasoning behind Herne's breaking of protocol appeared to be; not a selfish act, but a selfless one - for he was trying to find his kidnapped son - he couldn't pass on his legacy if there was no heir to the throne.
Herne then activates Jen's first form of the Ferai demon to help her in her quest, something Herne seemed to be already aware about her containing (earlier calling her a half-breed.)
The final encounter of Herne is after the battle Jared and Jen fight against the imposter Devena. Having unmasked her true form, Herne grabs the imposter and leaps from the cliff, destroying her and himself in the process and saving Solum from the grips of Chaos.
Herne is a Ferai unlike any other, which confirms his place as King no doubt. His horns are much larger and thicker, and indeed, more impressive than any other Ferai in the kingdom. However these are not the only set of horns he has, unlike other Ferai, Herne has two cheekbones that jut out, each containing a small boney horn. He appears to be blinded in his right eye, a dull white replaces where once was a pupil, showing his warring nature. Unlike other Ferai, Herne also has a large rugged beard which shows his age. However all of this pales in comparison to impressive height of King Herne. As Scree mentions, he is truly a warrior who has reached the height of his power, scaling in over 8ft tall, possibly higher, almost twice the size so it seems than his wife, Devena.
The name Herne comes from the English folk tale which features a character of the same name: Herne The Hunter. "Herne the Hunter" was a ghost who rode a ghost horse, but the most notable feature was of the antlers that grew from his head, very much like King Herne.