Moses
Numbers 1:20ESV·traditional attribution

The people of Reuben, Israel’s firstborn, their generations, by their clans, by their fathers’ houses, according to the number of names, head by head, every male from twenty years old and upward, all who were able to go to war:

John Calvin Reformed @genevareformer

20. And the children of Reuben, Israel’s eldest son If any disputatious person should contend that one family could not increase in 250 years to so great an amount, and thus should reject as nebulous what surpasses the ordinary rule of nature, we must bear in mind what I have already stated, that, inasmuch as this increase depended on the power of God, nothing is...

Matthew Henry Presbyterian @wholebiblehenry

We have here the speedy execution of the orders given for the numbering of the people. It was begun the same day that the orders were given, The first day of the second month; compare Num 1:18 with Num 1:1. Note, When any work is to be done for God it is good to set about it quickly, while the sense of duty is strong and pressing.

Commenting on Numbers 1:17-43

John Gill Reformed Baptist @doctorgill

And the children of Reuben, Israel's eldest son,.... Were numbered first, and next to them those of Simeon and Gad, for they were numbered according to the order in which they were to be encamped; for under Reuben's standard were Simeon and Gad, and under Judah's Issachar and Zebulun, and under Ephraim's Manasseh and Benjamin, and under Dan's Asher and Naphtali; and according to their...