Exodus 2:16 introduces Reuel (who was later Moses's father-in-law) as "a priest of Midian" without specifying anything further about which deity he was priest of:
Now a priest of Midian had seven daughters, and they came to draw water and fill the troughs to water their father's flock.
Is it known which deity he's associated with?
It was to Midian that Moses fled after slaying an Egyptian and where he married Zipporah the daughter of Jethro—also known as Reuel (Exod 2:11-22). Some speculate that worship of Yahweh originated in Midian, based on the fact that Jethro is called “the priest of Midian” and that the “mountain of God,” the place where Yahweh first appeared to Moses, is located in or close to Midian (Exod 3:1). These passages are thematically similar to other biblical texts that refer to Yahweh as coming from areas south of Palestine—not quite Midian but locations close to it, such as Edom, Seir, Sinai, and Teman. Is there any historical reality behind these allusions? Egyptian sources mentioning the name Yahweh as a place or tribal name of a people situated south of Canaan at the end of the second millennium BCE lend some credibility to these biblical references. The theory of the southern origins of Yahwism is thus known as the “Midianite hypothesis.” Juan Manuel Tebes, "Midian", n.p. [cited 16 Feb 2020]. Online: https://www.bibleodyssey.org:443/en/places/related-articles/midian
The midianites were children of Abraham through his concubine called Keturah
KJV Genesis 25:2,4-6 And she bare him Zimran, and Jokshan, and Medan, and Midian, and Ishbak, and Shuah... And the sons of Midian; Ephah, and Epher, and Hanoch, and Abidah, and Eldaah. All these were the children of Keturah. And Abraham gave all that he had unto Isaac. But unto the sons of the concubines, which Abraham had, Abraham gave gifts, and sent them away from Isaac his son, while he yet lived, eastward, unto the east country.
So Midian, along with his siblings, was sent away from Isaac with gifts for sustenance. The Bible says of Abraham:
KJV Genesis 18:19 For I know him, that he will command his children and his household after him, and they shall keep the way of the Lord, to do justice and judgment; that the Lord may bring upon Abraham that which he hath spoken of him.
All Abraham's children were brought up in the way of the Lord.
It is notable that there have been people worshipping God outside of Israel:
KJV Genesis 14:18 And Melchizedek king of Salem brought forth bread and wine: and he was the priest of the most high God.
As Midian was Abraham's son and was instructed in the way of the Lord, it is very very likely that Jethro was a priest of the Most High God.
Rueul is another name of Jethro, the father-in-law of Moses (Ex 2:18, 21, 3:1, 4:18, Num 10:29; see also Ex 18).
Jethro's actions in advising Moses, his preparation of sacrifices (as recorded in Ex 18) Jethro's position as priest in Midian, and his willingness to praise the LORD (Ex 18:1, 10) all indicate that he was priest of Jehovah = LORD God.
The name Reuel translates as "Friend of God".
Much like other Biblical names that end with "el" such as Michael, Daniel, and Israel, that "el" part is a shortening of one of God's titles.
Admittedly, not everyone's name indicates what they will do in life, but if that was one of the names he used, that at least indicates he was familiar with the idea.
As an aside, that same name is one of the Rs in J.R.R.Tolkien but not G.R.R.Martin.
According to the saying of Reuel "Now I know ' to me, that do not mean he was not Jehovah's priest, because so many of us now in the church as choir members and functioning in different department and believing Christ, were been born into this system which as not yet encounter the manifestation of Christ power, will also say like Reuel when ever they shall encounter this great power
