First son of Jacob and Leah (OT) (6)
I believe the answer is:
reuben
(Other definitions for reuben that I've seen before include "Son of Jacob; bee run (anag.)" , "one found in the first 6 [BOOK] of the 26 [BIBLE]" , "Jacob's eldest son" , "tribe" , "First son of Jacob (OT)" .)