I think the covenant was between Israel and God.
When the children of Israel arrived at Sinai that was the beginning of the nation of Israel.
God had set them apart from other nations and He asked for their obedience...... "if you will obey.......the you will be a special treasure to Me above all people; for all the earth is Mine". (Exodus 19:5-8). "And all the people answered All that the LORD has spoken we will do."
I think it was Moses
Moses
The second covenant was not made between God and Abraham. It was made between God & Moses at Mount Sinai. This is where the ten commandments originated.
The covenant with Moses is already made and most religions hold that you cannot intercede with the Dead for a new covenant.
Moses sealed the covenant by sacrificing animals and sprinkling their blood on the altar and the people. This ritual symbolized the binding agreement between God and the Israelites.
It doesn't have a "name", it was called a "staff". Moses was a shepherd, and shepherds used staffs to help them with their duties.
The covenant between God and the Israelites, with Moses serving as messenger, was made on the 5th of Sivan (late spring/early summer), 1312 BCE. Non-traditional opinions may place it at an earlier date.See also:More about the Israelite covenant
The solemn agreement between God and the Israelites is known as the "Covenant" or the "Covenant of Moses." It outlined the terms of their relationship, including God's promises to the Israelites and their responsibilities in return.
Moses
The three major Jewish covenants are Noah's Covenant, Abraham's Covenant, the Mosaic Covenant (Moses' Covenant.)
Moses
Judaism's roots are in the Hebrew religion of Abraham; and in the Israelite religion of Moses. According to tradition, "Judaism" as such began with the covenant between Abraham and God.