Aharon HaKohen, son of Amram and Yocheved, was the brother of Miriam and of Moses, his younger brother. He married Elisheba, daughter of Amminadab and sister of Nachshon, of the tribe of Judah; they had four sons, Nadav, Avihu, Elazar and Itamar.

While Moses grew up in Pharaoh's court, Aharon remained with his kinsmen in the land of Goshen. When Moses confronted Pharaoh, Aharon served as his spokesman, and his staff accompanied the signs that preceded the Exodus. The Sages teach that he merited the priesthood because he did not envy his younger brother but rejoiced in his mission.

The first Kohen Gadol, he received the priesthood for himself and his descendants: all Kohanim descend from him. On the day the Mishkan was inaugurated, his two eldest sons, Nadav and Avihu, died; he remained silent and accepted the divine decree. During Korach's rebellion his incense offering halted the plague, and his staff, which blossomed and bore almonds, confirmed the divine choice.

In Pirkei Avot, Hillel teaches: "Be of the disciples of Aaron, loving peace and pursuing peace." Avot de-Rabbi Natan describes how he would sit with each of two quarreling men in turn until they reconciled and embraced.

He died on the first of Av in the fortieth year after the Exodus, on Mount Hor, at the age of 123; it is the only date of death recorded in the Bible. Moses removed his high-priestly garments and placed them on his son Elazar, and the whole house of Israel mourned him for thirty days.