Aaron and his four sons were the first priests appointed as the priestly system was established by God.[7][8] The Levites as a tribe were later ordained for the priestly service after answering a call to take the LORD’s side after the idolatry centered around the golden calf.[9] After the death of Nadab and Abihu, Eleazar and Ithamar took their places as priests, because neither Nadab nor Abihu had any sons.[10][11][12][13]