When Moses’ father-in-law, Jethro, heard everything that God had done for the Israelites, he said:
Exodus 17:10-11 Praise the Lord … for he has rescued you from the Egyptians and from Pharaoh. Yes, he has rescued Israel from the powerful hand of Egypt! I know now that the Lord is greater than all other gods, because he rescued his people from the oppression of the proud Egyptians.
Jethro wasn’t just a father-in-law. He was also a high priest of Midian (Exodus 3:1). He effectively put God over any other god he served.
It’s consistent with God’s promise to the Israelites, before the plagues in Egypt started:
Exodus 6:6-7I am the Lord. I will free you from your oppression and will rescue you from your slavery in Egypt. I will redeem you with a powerful arm and great acts of judgment. I will claim you as my own people, and I will be your God. Then you will know that I am the Lord your God who has freed you from your oppression in Egypt.
And also with His promises about the Egyptians:
Exodus 7:5 When I raise my powerful hand and bring out the Israelites, the Egyptians will know that I am the Lord.