Hebrews 7:3 explains that we do not know anything about the beginning or end of Melchizedek’s life. He appears and disappears on the pages of Scripture.
Melchizedek served as “priest of God Most High” (Genesis 14:18). As priest, he served the only true God, the God of the Bible.
More than that, Melchizedek served as king (Genesis 14:18). That was unusual because a person served as a priest or a king but not both. By serving in those offices, Melchizedek pointed ahead to Jesus, who is Prophet, Priest and King.