John Gill Commentary Numbers 2:14

"And the tribe of Gad: and the prince of the children of Gad shall be Eliasaph the son of Reuel." — Numbers 2:14 (ASV)

Then the tribe of Gad
Who was placed on the other side of Reuben's standard, and according to the former direction he must be before, and Simeon behind; and Gad being the eldest son of Leah's handmaid Zilpah, is fitly placed under Leah's firstborn, and being the son of an handmaid, could not object to his situation:

and the captain of the sons of Gad [shall be]
Reuel :
who is called Deuel, (Numbers 1:14) (7:42) . The letters (r) , "resh", and (d) , "daleth", being similar, are sometimes put one for the other, of which there are other instances, as in (Genesis 10:3Genesis 10:4) , compared with (1 Chronicles 1:6 1 Chronicles 1:7) .