Aaron, the brother of Moses, was the first High Priest of Israel and patriarch of the family called Kohen. (This name is sometimes spelled Cohen; it comes from the Hebrew word for priest and, in biblical times, referred to those who conducted worship at the ancient Temple.)
When Moses, confronted by God at the burning bush, complained that his public speaking ability was not adequate for the task of calling on Pharaoh to release the Hebrew people from bondage in Egypt, his older brother Aaron was called upon to become his spokesman (Exodus, chapters 6 and 7). Thus it was that Aaron, standing before Pharaoh, performed the miracles of turning his staff into a serpent and calling forth the first three of ten plagues that persuaded Pharaoh to release the Hebrews.
In the wilderness journey following Passover, when the people of Israel complained about God's leadership, Aaron was named High Priest. As such, he conducted the first worship services held in the Tent of Meeting, sometimes called the Tabernacle in the Wilderness. The vestments he wore were made according to the instructions of God, and the ritual he instituted lasted for more than five hundred years, until the destruction of the Second Temple at Jerusalem in 70 CE.