Onto Reuben, Jacob's oldest son. He might be firstborn, but he forfeited his birthright because he slept with his dad's concubine. That's a pretty big no-no.
Reuben has a lot of sons who end up living in the Northern Kingdom when Israel splits into two after David dies. Eventually, these guys are forced into exile by the Assyrians.
Jacob's son, Gad, gets a little airtime, too, along with half of Manasseh's tribe (that's one of Jacob's grandsons).
Apparently, the descendants of Reuben, Gad, and Manasseh band together and fight all kinds of battles. They win some and they lose some. And they are all exiled together by the Assyrians, too.
So why was everyone exiled? Well, the folks from Manasseh's tribe did about the worst thing you could do back then and started worshipping other gods. Yahweh was not amused, so he nudged the king of Assyria to go attack the Northern Kingdom.
That's why Reuben, Gad, and Manasseh's tribes are mostly gone for good.