I have always heard that Melchizedek is Shem... Noah's first born son, and I also heard that the early Church also believed this... interesting read, but I don't think the good father is correct...
I like the theory of Shem much better.
Found this in the 1913 Catholic Encyclopedia:
The Rabbins identified Melchisedech with Sem, son of Noe, rather for polemic than historic reasons, since they wished to set themselves against what is said of him as a type of Christ "without father, without mother, without genealogy" (Hebrews 7:3).