Moses' father-in-law Jethro was the priest of Midian. He heard about everything God had done for Moses and for his people Israel. He heard how the LORD had brought Israel out of Egypt.
References for Exodus 18:1
Moses had sent his wife Zipporah to his father-in-law. So Jethro welcomed her
and her two sons. One son was named Gershom. That's because Moses had said, "I'm an outsider in a strange land."
The other was named Eliezer. That's because Moses had said, "My father's God helped me. He saved me from Pharaoh's sword."
Moses' father-in-law Jethro came to Moses in the desert. Moses' sons and wife came with Jethro. Moses was camped near the mountain of God.
Jethro had sent a message to him. It said, "I, your father-in-law Jethro, am coming to you. I'm bringing your wife and her two sons."