Who was Reuben?
Reuben was the oldest son of Jacob.
This verse seems to suggest two derivations of the name. As it stands in Massoretic Text it means "behold a son"; but the reason given for so calling him is "The Lord hath looked upon my affliction," which in Hebrew is Heb: ra'ah be`onyi, literally, "He hath seen my affliction." Of his boyhood we have only the story of the mandrakes (Gen 30:14).
As the firstborn he should really have been leader among his father's sons. His birthright was forfeited by a deed of peculiar infamy (Gen 35:22), and as far as we know his tribe never took the lead in Israel. It is named first, indeed, in Nu 1:5,20, but thereafter it falls to the fourth place, Judah taking the first (Nu 2:10, etc.).
To Reuben's intervention Joseph owed his escape from the fate proposed by his other brethren (Gen 37:29). Some have thought Reuben designed to set him free, from a desire to rehabilitate himself with his father. But there is no need to deny to Reuben certain noble and chivalrous qualities.
Jacob seems to have appreciated these, and, perhaps, therefore all the more deeply lamented the lapse that spoiled his life (Gen 49:3 f). It was Reuben who felt that their perils and anxieties in Egypt were a fit recompense for the unbrotherly conduct (Gen 42:22). To assure his father of Benjamin's safe return from Egypt, whither Joseph required him to be taken, Reuben was ready to pledge his own two sons (Gen 42:37). Four sons born to him in Canaan went down with Reuben at the descent of Israel into Egypt (Gen 46:8 f).
IBSE, "Reuben" (in the public domain) with minor edits.