Nanafushi

was a ninja who hailed from the Land of Valleys.

Part I
He was set to steal Konoha's secrets. He used the Transformation Technique to disguise himself as Might Guy. As he entered the village, Naruto thought he was the real Might Guy and took him to Rock Lee's dojo. After a few fights the real Might Guy returned and fought Nanafushi (who concealed himself as Rock Lee by using the Transformation Technique again). Then later after finding out who he really was, they took him in to Tsunade to be detained.