Treasury of Scripture Knowledge
And the children of Reuben, Israel's eldest son, by their generations, after their families, by the house of their fathers, according to the number of the names, by their polls, every male from twenty years old and upward, all that were able to go forth to war;
"On the south will be the divisions of the camp of Reuben under their standard. The leader of the people of Reuben is Elizur son of Shedeur.
Reuben was the firstborn of Israel. The Reubenites: from Hanoch, the family of the Hanochites; from Pallu, the family of the Palluites;
So Leah became pregnant and gave birth to a son. She named him Reuben, for she said, "The Lord has looked with pity on my oppressed condition. Surely my husband will love me now."
The sons of Reuben: Hanoch, Pallu, Hezron, and Carmi.
Reuben, you are my firstborn, my might and the beginning of my strength, outstanding in dignity, outstanding in power.
1 Chronicles 5:1
The sons of Reuben, Israel's firstborn -- (Now he was the firstborn, but when he defiled his father's bed, his rights as firstborn were given to the sons of Joseph, Israel's son. So Reuben is not listed as firstborn in the genealogical records.