Who was the Lawgiver at Mount Sinai?

God.

PS you sure ask a lot of questions.

The LORD gave the law to Moses, and Moses gave the law to the children of Israel: "And Moses went up to God and the LORD called to him out of the mountain saying, 'Thus you shall say to the house of Jacob, and tell the children of Israel...(Exodus 19:3).'"

"And Moses turned and went down from the mountain, and the two tablets of the Testimony were in his hand. The tablets were written on both sides; on the one side and on the other they were written. Now the tablets were the work of God and the writing was the writing of God engraved on the tablets (Exodus 32:15-16)."

"And the LORD delivered to me two tablets of stone written with the finger of God, and on them were all the words which the LORD had spoken to you on the mountain from the midst of the fire in the day of the assembly (Deu 9:10)."

"And He declared to you His covenant which He commanded you to perform, the Ten Commandments; and He wrote them on two tablets of stone. And the LORD commandmed me at that time to teach you statutes and judgments, that you might observe them in the land which you cross over to possess (Deu 4:13-14)."

"At that time the LORD said to me, 'Hew for yourself two tablets of stone like the first, and come up to Me on the mountain and mark yourself an ark of wood. And I will write on the tablets the words that were on the first tablets, which you broke; and you shall put them in the ark.' So I made an ark of acacia wood, hewed two tablets of stone like the first, and went up the mountain, having two tablets in my hand. And He wrote on the tablets according to the first writing, the Ten Commandments, which the LORD had spoken to you in the mountain from the midst of the fire in the day of the assembly; and the LORD gave them to me. Then I turned and came down from the mountain, and put the tablets in the ark which I had made; and there they, just as the LORD commanded me (Deu 10:1-5)."

Yahshua (Jesus) was with them, and he gave them the law.

1 Corinthians 10:1-4 For I do not wish you to be ignorant, brothers, that all our fathers were under the cloud, and all passed through the sea, (2) and all were immersed into Mosheh in the cloud and in the sea, (3) and all ate the same spiritual food, (4) and all drank the same spiritual drink. For they drank of that spiritual Rock that followed, and the Rock was Messiah.

Jehovah, God the Almighty, gave Moses the Ten Commandments on Mt. Sinai. It was Jehovah's finger that wrote the law on the tables of stone.

Hammurabi