Who was the priest-king of Salem who blessed Abram?

Answer: Melchizedek

Melchizedek, king of Salem and priest of God Most High, blessed Abram.

“Then Melchizedek king of Salem brought out bread and wine—since he was priest of God Most High— and he blessed Abram and said: “Blessed be Abram by God Most High, Creator of heaven and earth,”— Genesis 14:18-19 (BSB)