Moses
Deuteronomy 5:5ESV·traditional attribution

while I stood between the LORD and you at that time, to declare to you the word of the LORD. For you were afraid because of the fire, and you did not go up into the mountain. He said:

Matthew Henry Presbyterian @wholebiblehenry

Here, 1. Moses summons the assembly. He called all Israel; not only the elders, but, it is likely, as many of the people as could come within hearing, Deu 5:1. The greatest of them were not above God's command, nor the meanest of them below his cognizance; but they were all bound to do. 2.

Commenting on Deuteronomy 5:1-5

John Gill Reformed Baptist @doctorgill

I am the Lord thy God,.... This is the preface to the ten commandments, and is the same with that in Exo 20:2; see Gill on Exo 20:2, and those commands are here delivered in the same order, and pretty near in the same words, with a little variation, and a few additions; which I shall only observe, and refer to Exo 20:1 for the sense of the various laws.

Jamieson-Fausset-Brown Reformed @jfbcommentary

I stood between the Lord and you at that time--as the messenger and interpreter of thy heavenly King, bringing near two objects formerly removed from each other at a vast distance, namely, God and the people (Gal 3:19). In this character Moses was a type of Christ, who is the only mediator between God and men (Ti1 2:5), the Mediator of a better covenant (Heb 8:6; Heb 9:15; Heb 12:24).