"When she became Mother of the Creator, she truly became Queen of every creature." - Saint John Damascene
The Feast of the Queenship of Mary is a feast day that celebrates Queenship of the Virgin Mary.
The feast day was first created by Pope Pius XII in his encyclical Ad caeli reginam. The title of Queen of Heaven is heavily based on her role as Theotokos , a title given to her at the Council of Ephesus in 431 AD. An even earlier text from Origen gave her the title Dormina, the feminie form of dominus or Lord. Even farther back, to the time of King David, many sources record that the Mother of the King, the gebirah (Great Lady) held great power as advocate to the King. It is often pointed out in 1 Kings 2:20, as King Solomon's mother is seated on a throne at his right -
"Make your request, Mother, for I will not refuse you."
In his 1946 radio message, Pope Pius XII explained more on the theological reasons for her title as Queen:
He, the Son of God, reflects on His heavenly Mother the glory, the majesty and the dominion of His kingship, for, having been associated to the King of Martyrs in the ... work of human Redemption as Mother and cooperator, she remains forever associated to Him, with a practically unlimited power, in the distribution of the graces which flow from the Redemption. Jesus is King throughout all eternity by nature and by right of conquest: through Him, with Him, and subordinate to Him, Mary is Queen by grace, by divine relationship, by right of conquest, and by singular choice [of the Father]
And later, in his encyclical :
From the earliest ages of the Catholic Church a Christian people, whether in time of triumph or more especially in time of crisis, has addressed prayers of petition and hymns of praise and veneration to the Queen of Heaven and never has that hope wavered which they placed in the Mother of the Divine King, Jesus Christ; nor has that faith ever failed by which we are taught that Mary, the Virgin Mother of God, reigns with a mother's solicitude over the entire world, just as she is crowned in heavenly blessedness with the glory of a Queen.
All four Marian anitphons express the queenship of Mary - the Salve Regina, Ave Regina caelorum, Alma Redemptoris Mater, and the Regina Caeli.
Originally celebrated on May 31st, the last day of the Marian month, Pope Pius XII led a large procession in Rome and crowned the Salus Populi Romani icon of Mary in Rome. The feast was moved to August 22nd in 1969 by Pope Paul VI so that it would fall on the former Octave day of the Assumption. This move was done to emphasize the close bond between her Queenship and her glorification in body and soul next to Christ, her Son.