What was the name of Moses' father-in-law, the priest of Midian?

Answer: Jethro

Moses shepherded the flock of his father-in-law Jethro, the priest of Midian (called Reuel in Exodus 2:18).

“Meanwhile, Moses was shepherding the flock of his father-in-law Jethro, the priest of Midian. He led the flock to the far side of the wilderness and came to Horeb, the mountain of God.”— Exodus 3:1 (BSB)