The corruption out of Angmar has angered and misguided many of the creatures in The North Downs, including Valikas, whose temptation of Angmarim riches has blackened his heart.
'Since some of the Earth-kin have sided with Angmar, their minds have slowly warped. One Earth-kin, called Valikas, walked an even darker path. He trained with the Angmarim and now seeks to corrupt his fellow Jorkyn to the ways of the Witch-king of Angmar. There is no path back to the light for Valikas. He must be dealt with.'
Valikas can be found somewhere in The North Downs.
You should defeat Valikas.