Kristoff is the rightful heir to the Horde and current king of the Forbearer Army, which he created. Shortly after his birth, his uncle Demestriu attempted to have him killed. Kristoff was hidden and raised by human guardians, living among them for centuries while learning little about the Lore.
Kristoff the Gravewalker created his Forebearer army by trolling human battle grounds and converting the strongest or most intellegent soldiers. The soldiers were only allowed to join if they pledge eternal loyalty to their new king.