According to the Torah, the tribe was founded by an individual, Reuben, the first son of Jacob, and a son of Leah, from whom it took its name; however some Biblical scholars view this as a postdiction, an eponymous metaphor providing an aetiology of the connectedness of the tribe to others in the Israelite confederation. With Leah as a matriarch, Biblical scholars regard the tribe as having been believed by the text's authors to have been part of the original Israelite confederation.
In the biblical account, Reuben are portrayed as having arrived east of the Jordan after leaving Egypt, but rather than taking land on the west of the Jordan, after conquering it under Joshua, instead took land on the east, as they owned a large number of cattle, and the territory seemed suitable for pasture. Israel Finkelstein et al., however, have claimed that lack of evidence for a systematic conquest or the abrupt appearance of a new culture indicates that the Israelites simply arose as a subculture within Canaanite society. The territory of Reuben encapsulated the territory of the earlier kingdom of Sihon.
According to the ancient Song of Deborah, Reuben declined to take part in the war against Sisera, the people instead idly resting among their flocks as if it were a time of peace, though the decision to do so was taken with a heavy heart. On the other hand, according to the Book of Chronicles, Reuben instigated a war with the Hagarites, and was victorious; in another portion of the same text, Reuben are said to have been assisted in this war by Gad and the eastern half of Manasseh. In the Blessing of Jacob, which some textual scholars date substantially later than these events, the tribe is characterised as fickle - unstable as water, and condemned to dwindle in power and size due to the incest of its eponymous founder; this incest is abruptly mentioned in the poem, without explaining the circumstances or the identity of the other party, nor are these details given elsewhere in the surviving text of the Bible, from which the episode appears to have been excised by the redactor.
As part of the Kingdom of Israel, the territory of Reuben was conquered by the Assyrians, and the tribe exiled; the manner of their exile lead to their further history being lost.