Reuben (Hebrew: רְאוּבֵן; Modern: Re'uven; Tiberian: Rəʾûḇēn) is the first and eldest son of Jacob (latter named by Hashem as Israel), with Leah. He is also the father of the Ancient Israelite Tribe of Reuben and of the Reubenites.
And Leah conceived, and bare a son, and she called his name Reuben: for she said, Surely Yahweh hath looked upon my affliction; now therefore my husband will love me.
Genesis 29:32
The Prophetic Blessing of Jacob, prior to his death:
And Jacob called unto his sons, and said, Gather yourselves together, that I may tell you that which shall befall you in the last days. Gather yourselves together, and hear, ye sons of Jacob; and hearken unto Israel your father. Reuben, thou art my firstborn, my might, and the beginning of my strength, the excellency of dignity, and the excellency of power: Unstable as water, thou shalt not excel; because thou wentest up to thy father's bed; then defiledst thou it: he went up to my couch.
Genesis 49:1-4
The Tribe of Reuben
The Tribe of Reuben (Hebrew: שֵׁבֶט רְאוּבֵן; Modern: Shevet Re'uven; Tiberian: Šḗḇeṭ Rəʼûḇēn) is one of the Twelve Tribes of Israel.
For Tribe allotment see: Joshua 13:15-23