Auru is another member of Telma's Resistance, and is probably the oldest among them. He is interested and wise about the desert and the evils within it. He also possibly could have known the Ancient Sages that guard the Mirror of Twilight, and also knew that they had tutored Princess Zelda. Link first meets him in Lake Hylia atop a lookout tower. He claims that the evil destroying Hyrule is coming from the desert, more specifically, Arbiter's Grounds, an old prison for the worst of the worst. He gives Link a memo calling in an old debt so that Fyer allows him to use his cannon to get to the Gerudo Desert.
After meeting Auru there, Link can find him later at Telma's Bar.