While Joshua was engaged in battle with the Amalekites at Rephidim, "Moses climbed to the top of the hill with Aaron and Hur. As long as Moses kept his hands raised up, Israel had the better of the fight, but when he let his hands rest , Amalek had the better of the fight. Moses hands however, grew tired, so they put a rock in place for him to sit on. Meanwhile Aaron and Hur supported his hands, one on one side and one on the other, so that his hands remained steady till sunset. And Joshua mowed down Amalek and his people with the edge of the sword." (Exodus 17:10-13).
Hur was a leader of Israel during the years in the desert. He, along with Aaron was left in charge of the people while Moses went up on Mount Sinai (Exodus 24:14).
Next person in the Bible: Hushai