Blessed Virgin Mary

Our Precious Mother Mary gave St. Dominic the Rosary Prayer in 1214

History
In 1214, the Virgin Mary appeared to a penitent St. Dominic, she presented the Rosary as the greatest weapon for conversion. Immediately, bells rang miraculously to summon the people to hear Dominic. While preaching on the Rosary, a statue of the Virgin raised its arms three times seeming calling down God's vengeance on the unrepentant and and a violent storm erupted. Many heretics returned to the Church, and Dominic began to spread this powerful new devotion.
The Rosary eclipsed and incorporated earlier devotional practices such as the saying of 150 'Our Fathers' to parallel the more involved monastic practice of saying all 150 Psalms, and the use of rocks (later beads) to keep track of the repetitions.
The Rosary Solves All Problems
Regarding the Holy Rosary, Sister Lucia (the lone surviving seer of Fatima) speaking to Father Fuentes in the authentic
December 26, 1957 interview said:
"Look, Father, the Most Holy Virgin in these last times in which we live has given new efficacy in the
recitation of the Holy Rosary.

There is no problem, I tell you, no matter how difficult it is, that we cannot solve by the prayer of the Holy Rosary. With the Holy Rosary, we will save ourselves. We will sanctify ourselves. We will console Our Lord and obtain the salvation of many souls."
 
Prayers
Spring, 1916:
The Angel's Prayer
"My God, I believe, I adore, and I love You! I beg pardon of You for those who do not believe, do not adore, do not hope and do not love You!"

October, 1916: The Angel's Second Prayer
"Most Holy Trinity, Father, Son, Holy Spirit, I adore You profoundly and offer You the most Precious Body, Blood, Soul and Divinity of Jesus Christ, present in all the tabernacles of the earth, in reparation for the outrages, sacrileges, and indifference with which He Himself is offended. And through the infinite merits of His Most Sacred Heart and of the Immaculate Heart of Mary,
I beg of You the conversion of poor sinners."

Fatima, Portugal, 1917
Apparitions to 3 children of Fatima

Devotions
May 13, 1917: Mary's Request for the Daily Rosary
"Pray the Rosary every day, in order to obtain peace for the world, and the end of the war."

Prayers
May 13, 1917: Children's Interior
 'Impulse' Prayer from the
Virgin Mary
"O most Holy Trinity, I adore You! My God, my God,
 I love You in the most Blessed Sacrament."
 

July 13, 1917:
Mary's Request for Sacrifice
"Sacrifice yourselves for sinners, and repeat often, especially whenever you make a sacrifice for them:
'O Jesus, it is for love of You, for the conversion of sinners and in reparation for the sins
committed against the Immaculate Heart of Mary.'"

 The 'Hail Mary' eventually became longer
(the second half of the prayer being added in the 14th/15th century).

July 13, 1917, The Virgin Mary's Rosary Ejaculation'
"O my Jesus, forgive us, save us from the fire of Hell. Lead all souls to Heaven, especially those in most need of your Mercy." was added at the request of Mary speaking through Sister Lucia, one of the seers of the 1917 apparition of
Mary in Fatima.
 The Rosary is also called the
 'New Psalter of the Virgin'

It is difficult to find a pope or saint who has not had something to write, or say, about the value of the Rosary. Every pope of the 20th century wrote something to encourage the devotion.