Each tribe is said to be descended from one of the sons of the Biblical patriarch Jacob (younger son of Isaac, and grandson of Abraham). They are conventionally listed in the order of the sons' ages – eldest first. Reuben was the eldest son, and Benjamin the youngest.
According to Wikipedia: "From what is known of Jacob, he had two wives, sisters Leah and Rachel, and two mistresses, sisters Bilhah and Zilpah, by whom he had at least thirteen children. Though it is possible he may have had more sons and daughters than what is recorded in surviving texts, only twelve sons would form the basis for the twelve tribes of Israel ... Jacob was known to display favoritism among his children, particularly for Joseph and Benjamin, the sons of his favorite wife, Rachel, and so, the tribes themselves were not treated equally in a divine sense. Joseph, despite being the second–youngest son, received double the inheritance of his brothers, treated as if he were the firstborn son instead of Reuben, and so, his tribe was later split into two tribes, named for his sons, Ephraim and Manasseh".
Jacob's first wife, Leah, was the mother of six of the sons in question – the first four (Reuben, Simeon, Levi and Judah), and the ninth and tenth (Issachar and Zebulun). Bilhah was the mother of his fifth and sixth sons (Dan and Naphtali), and Zilpah the seventh and eighth (Gad and Asher). As already mentioned, Rachel was the mother of Jacob's favourite sons, Joseph and Benjamin (the two youngest of the twelve).
© Haydn Thompson 2021