For Christ is called a high priest after the order of Melchisedec. “And being made perfect, he became the author of eternal salvation unto all them that obey him;” - Hebrews 5:9
“Whither the forerunner is for us entered, even Jesus, made an high priest for ever after the order of Melchisedec.” - Hebrews 6:20
But who is Melchizedek? Of Melchizedek we read that “he was the priest of the most high God." (see Genesis 14:18-24) Melchizedek was the king of Salem who offered bread and wine to Abram. He blessed Abram* and he blessed God who had delivered the enemies into the hand of Abram.
“For this Melchisedec, king of Salem, priest of the most high God, who met Abraham returning from the slaughter of the kings, and blessed him; To whom also Abraham gave a tenth part of all; first being by interpretation King of righteousness, and after that also King of Salem, which is, King of peace;” - Hebrews 7:1-2
*(Abram, who later became Abraham in Genesis 17:5-7)
(also see Hebrews 5:6-10, 6:20, 7:17, 21, Psalm 110:4)