Who is Mechisedec and his role in God's kingdom?

Melchizedek is a person from the Old Testament who as king and priest reminds us of Jesus and some believe was the Pre-incarnate Jesus Christ.

In the Authorised King James Version of 1611 he appeared as Melchizedek in the Old Testament and Melchisedec in the New Testament.

In either case, Melchizedek was introduced as king of Salem (now called Jerusalem) and priest of the Most High that encountered Abraham in Genesis 14:18-20.

In Book of Hebrews, Jesus is described as a priest forever from the order of Melchizedek.