Genesis 14:
18 And Melchizedek king of Salem brought forth bread and wine: and he was the priest of the most high God.
19 And he blessed him, and said, Blessed be Abram of the most high God, possessor of heaven and earth:
20 And blessed be the most high God, which hath delivered thine enemies into thy hand. And he gave him tithes of all.
And again in Hebrews 7:
1 For this Melchisedec, king of Salem, priest of the most high God, who met Abraham returning from the slaughter of the kings, and blessed him;
2 To whom also Abraham gave a tenth part of all; first being by interpretation King of righteousness, and after that also King of Salem, which is, King of peace;
4 Now consider how great this man was, unto whom even the patriarch Abraham gave the tenth of the spoils.
5 And verily they that are of the sons of Levi, who receive the office of the priesthood, have a commandment to take tithes of the people according to the law, that is, of their brethren, though they come out of the loins of Abraham:
6 But he whose descent is not counted from them received tithes of Abraham, and blessed him that had the promises.
7 And without all contradiction the less is blessed of the better.
Clearly if you thought Melchisedec was just a king then you do not really know about him.