My friend Mel

Here is the rest of Genesis 14.

¹⁷ After Abram returned from defeating Kedorlaomer and the kings allied with him, the king of Sodom came out to meet him in the Valley of Shaveh (that is, the King’s Valley).
¹⁸ Then Melchizedek king of Salem brought out bread and wine. He was priest of God Most High, ¹⁹ and he blessed Abram, saying,

“Blessed be Abram by God Most High,
    Creator of heaven and earth.
²⁰ And praise be to God Most High,
    who delivered your enemies into your hand.”

Then Abram gave him a tenth of everything.

²¹ The king of Sodom said to Abram, “Give me the people and keep the goods for yourself.”
²² But Abram said to the king of Sodom, “With raised hand I have sworn an oath to the Lord, God Most High, Creator of heaven and earth, ²³ that I will accept nothing belonging to you, not even a thread or the strap of a sandal, so that you will never be able to say, ‘I made Abram rich.’ ²⁴ I will accept nothing but what my men have eaten and the share that belongs to the men who went with me—to Aner, Eshkol and Mamre. Let them have their share.”

First of all, I must point out that the translators of the NIV have cleaned up an embarrassment. In the original Hebrew, it is completely ambiguous whether Abram gives the tithe to Melchizedek, or Melchizedek gives it to Abram. Many commonly used translations preserve this ambiguity, but the NIV just adopts the more common understanding. The literal translation of the phrase is just "He gave him tithe of all," with no clarity as to who "He" is. The idea appears to be that since Melchizedek is the "priest of God Most High," he gets to collect a fee in exchange for Abram's victory. Thus we have the prototype for hucksters everywhere, from Jim Bakker to Reverend Ike.

In the New Testament book Hebrews, we learn that:

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;

7:2 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;

7:3 Without father, without mother, without descent, having neither beginning of days, nor end of life; but made like unto the Son of God; abideth a priest continually.

7:4 Now consider how great this man was, unto whom even the patriarch Abraham gave the tenth of the spoils.

So he was never born, God just conjured him up for the occasion. And apparently he's still around. The idea is supposed to be that he somehow prefigures Jesus. A psalm also suggests that Mel is a prototype for the Messiah. But here he is still hogging a tenth of Abram's loot.