There is a tradition in the church (based on a statement in the Lectures on Faith) that Melchizedek was Shem, son of Noah. While this may or may not be true, there is a great deal more that we know about him from the Joseph Smith Translation of the bible. For example, we know that:
He had strong faith, and even as a child stopped the mouths of lions.
Through his faith, he quenched the violence of fire.
He was a high priest in the Melchizedek (or Holy) priesthood.
He was the King of Salem, and was called a prince of peace.
He and his people sought to join their city with that of Enoch.
Having obtained such peace, he was called by his people the king of heaven, or the King of peace.
He was keeper of the storehouse of God, and collected the tithes of the people.
Obviously, Melchizedek was a great man, and though we know little about the details of these facts, they certainly cast a light on the righteousness of the man, and his closeness to the Lord.
Here’s the record:
25 And Melchizedek lifted up his voice and blessed Abram.
26 Now Melchizedek was a man of faith, who wrought righteousness; and when a child he feared God, and stopped the mouths of lions, and quenched the violence of fire.
27 And thus, having been approved of God, he was ordained an high priest after the order of the covenant which God made with Enoch,
28 It being after the order of the Son of God; which order came, not by man, nor the will of man; neither by father nor mother; neither by beginning of days nor end of years; but of God;
29 And it was delivered unto men by the calling of his own voice, according to his own will, unto as many as believed on his name.
30 For God having sworn unto Enoch and unto his seed with an oath by himself; that every one being ordained after this order and calling should have power, by faith, to break mountains, to divide the seas, to dry up waters, to turn them out of their course;
31 To put at defiance the armies of nations, to divide the earth, to break every band, to stand in the presence of God; to do all things according to his will, according to his command, subdue principalities and powers; and this by the will of the Son of God which was from before the foundation of the world.
32 And men having this faith, coming up unto this order of God, were translated and taken up into heaven.
33 And now, Melchizedek was a priest of this order; therefore he obtained peace in Salem, and was called the Prince of peace.
34 And his people wrought righteousness, and obtained heaven, and sought for the city of Enoch which God had before taken, separating it from the earth, having reserved it unto the latter days, or the end of the world;
35 And hath said, and sworn with an oath, that the heavens and the earth should come together; and the sons of God should be tried so as by fire.
36 And this Melchizedek, having thus established righteousness, was called the king of heaven by his people, or, in other words, the King of peace.
37 And he lifted up his voice, and he blessed Abram, being the high priest, and the keeper of the storehouse of God;
38 Him whom God had appointed to receive tithes for the poor.
39 Wherefore, Abram paid unto him tithes of all that he had, of all the riches which he possessed, which God had given him more than that which he had need.
40 And it came to pass, that God blessed Abram, and gave unto him riches, and honor, and lands for an everlasting possession; according to the covenant which he had made, and according to the blessing wherewith Melchizedek had blessed him.