Lord Gntaru (Gntarl) is the Admiral of the United Army and is in charge of leading the war against the Magical Kingdom under the direction of the Elders.
After discovering that Munto has gone into the Lower World, Gntarl suspects that he has done so in an effort to save the Magical Kingdom and sends the Akuto warrior after him in an attempt to finish him off before he has a chance to accomplish his goal.
Note: His name is spelled Ga (ガ) n' (ン) taa (ター) ru (ル) in the anime which is pronounced as Gntarl (Source: Ep 1 @ ~13:20).