Kakoi

Kakoi has shoulder-length brown hair and unique markings under his eye. He wears a high-collared white tunic and white hat.

In the anime, the Third Hokage reported to Kakashi that someone had been slipping through Konoha's Sensing Barrier. Kakoi reported that the possibilities were that there was a traitor who had knowledge of how not to trigger it, of that someone had a jutsu that could break through it. He showed Kakashi reports where the barrier was on high alert, around the self-governing Uchiha district. Hiruzen tasked Kakashi with installing a sensing barrier there without linking back to the Anbu.