"All power in heaven and on earth has been given to me." (Matthew 28:18)
In his encyclical Quas primas, written in 1925, Pope Pius XI declared the last Sunday of the Month of October to be a feast day titled Domini Nostri Jesu Christi Regis (Our Lord Jesus Christ the King). The encyclical was a response to growing nationalism and secularism in the world during this time and reminds us that truly, the King of the world, universe and all in it is Jesus Christ. In the encyclical among many other references to Sacred Scripture, Pope Pius XI also quotes Isiah:
"For a child is born to us and a son is given to us, and the government is upon his shoulder, and his name shall be called Wonderful, Counselor, God the mighty, the Father of the world to come, the Prince of Peace. His empire shall be multiplied, and there shall be no end of peace. He shall sit upon the throne of David and upon his kingdom; to establish it and strengthen it with judgment and with justice, from henceforth and for ever."
Furthermore, Pope Pius XI writes in the encyclical :
"If to Christ our Lord is given all power in heaven and on earth; if all men, purchased by his precious blood, are by a new right subjected to his dominion; if this power embraces all men, it must be clear that not one of our faculties is exempt from his empire. He must reign in our minds, which should assent with perfect submission and firm belief to revealed truths and to the doctrines of Christ. He must reign in our wills, which should obey the laws and precepts of God. He must reign in our hearts, which should spurn natural desires and love God above all things, and cleave to him alone. He must reign in our bodies and in our members, which should serve as instruments for the interior sanctification of our souls, or to use the words of the Apostle Paul, as instruments of justice unto God."
In 1960, Pope John XXIII's revision of the calendar had the date and title unchanged, but upgraded the feast to a feast of the first class. In 1969, Pope Paul VI amended the title of the feast to "Domini Nostri Iesu Christi universorum Regis" or Our Lord Jesus Christ King of the Universe and moved the date from October 25th to the final Sunday of the liturgical year, immediately prior to the First Sunday of Advent. He assigned the feast it's highest ranking - a Solemnity. The liturgical vestments are those of joyous feasts - white or gold. It should be noted that the extraordinary form still celebrates the feast on October 25th.