Melchizedek was the king of Salem during the time of Abraham. He is briefly mentioned in Genesis as having offered a sacrifice of bread and wine to God, and he blessed Abraham.
He is a mysterious figure, but the key teaching of the Church is that Melchizedek was an early type or prefigurement of the Christ, who would be both a king and a high priest—a combination of roles which was generally rejected by the Jews. Some of the Church Fathers believed that Melchizedek was actually a manifestation of the second Person of the Trinity, pre-incarnate Son of God.
From the time of the Apostles, connections have been drawn between Melchizedek and Christ. In Hebrews (7:1-3), Saint Paul writes: "For this Melchizedek, king of Salem, priest of the Most High God, met Abraham returning from the slaughter of the kings and blessed him; and to him Abraham appointed a tenth part of everything. He is first, by translation of his name, king of righteousness, and he is also king of Salem, that is, king of peace. He is without father or mother or genealogy, and has neither beginning of days nor end of life, but resembling the Son of God, he continues a priest forever."
The Righteous Melchizedek is commemorated on May 22 and again among all the Old Testament righteous on the Sunday Before the Nativity.