Reuben was the firstborn of Israel. These were the descendants of Reuben: The Hanochite clan from Hanoch, the Palluite clan from Pallu,

Genesis 46:8
Now these are the names of the sons of Israel (Jacob and his descendants) who went to Egypt: Reuben, Jacob's firstborn.

Exodus 6:14
These were the heads of their fathers' houses: The sons of Reuben, the firstborn of Israel, were Hanoch and Pallu, Hezron and Carmi. These were the clans of Reuben.

Numbers 1:20
From the sons of Reuben, the firstborn of Israel, according to the records of their clans and families, counting one by one the names of every male twenty years of age or older who could serve in the army,

Numbers 26:4
"Take a census of the men twenty years of age or older, as the LORD has commanded Moses." And these were the Israelites who came out of the land of Egypt:

Numbers 26:6
the Hezronite clan from Hezron, and the Carmite clan from Carmi.

1 Chronicles 5:3
The sons of Reuben, the firstborn of Israel: Hanoch, Pallu, Hezron, and Carmi.

Reuben, the oldest son of Israel: the children of Reuben; Hanoch, of whom comes the family of the Hanochites: of Pallu, the family of the Palluites: