Melchizedekis a character in the Old Testament who appeared in Genesis to the patriarch Abraham. He is called "king of Salem" (believed to be ancient Jerusalem) and "priest of the most high God" in Genesis 14:18.
In the Tanakh, Melchizedek brought bread and wine to Abraham (then called Abram) after Abraham's victory over the four kings who had besieged Sodom and Gomorrah and had taken his nephew Lot prisoner (described in Genesis 14). (Gen. 14:18.) Melchizedek blessed Abraham in the name of ³God Most High, Creator of heaven and earth.² (Gen. 14:19.) In return, Abraham gave Melchizedek a tenth, a tithe, of the spoils gained from the battle. (Gen. 14:20.)
In some translations, Psalm 110:4 names Melchizedek as representative of the priestly line through which a future king of Israel's Davidic line was ordained. Alternatively, the term in Psalm 110:4 can be read ³rightful king.² (E.g., New JPS Tanakh.)
In Rabbinic interpretationIn the Midrash, the Rabbis identified Melchizedek with Shem son of Noah. (E.g., B. Talmud Nedarim 32b; Genesis Rabbah 46:7; Genesis Rabbah 56:10; Leviticus Rabbah 25:6; Numbers Rabbah 4:8.) Rabbi Isaac the Babylonian said that Melchizedek was born circumcised.
(Genesis Rabbah 43:6.) Melchizedek called Jerusalem 'Salem.' (Genesis Rabbah 56:10.)
The Rabbis said that Melchizedek instructed Abraham in the Torah. (Genesis Rabbah 43:6.)
Rabbi Eleazar said that Melchizedek's school was one of three places where the Holy Spirit manifested itself. (B. Talmud Makkot 23b.)
The Rabbis taught that Melchizedek acted as a priest and handed down Adam¹s robes to Abraham. (Numbers Rabbah 4:8.)
Rabbi Zechariah said on Rabbi Ishmael's authority that God intended to bring forth the priesthood through Melchizedek¹s descendants, but because Melchizedek blessed Abraham before he blessed God (in Gen. 14:19-20), God brought the priesthood forth from Abraham¹s descendants. (B. Talmud Nedarim 32b.)
Rabbi Judah said in Rabbi Nehorai's name that Melchizedek¹s blessing yielded prosperity for Abraham, Isaac, and Jacob. (Genesis Rabbah 43:8.) Ephraim Miksha'ah the disciple of Rabbi Meir said in the latter's name that Tamar descended from Melchizedek. (Genesis Rabbah 85:10.)Rabbi Hana bar Bizna citing Rabbi Simeon Hasida identified Melchizedek as one of the four craftsmen of whom Zechariah wrote in Zechariah 2:3. (B. Talmud Sukkah 52b; see also Song of Songs Rabbah 2:33 (crediting Rabbi Berekiah in the name of Rabbi Isaac).)
The Talmud teaches that David wrote the Book of Psalms, including in it the work of the elders, including Melchizedek (in Psalm 110). (B. Talmud Baba Batra 14b-15a.)
The Zohar finds in 'Melchizedek king of Salem' a reference to 'the King Who rules with complete sovereignty,' or according to another explanation, that 'Melchizedek' alludes to the lower world and 'king of Salem' to the upper world. (Zohar, Bereshit, 1:86b-87a:)
Source : http://www.crystalinks.com/melchizedek.html