Dominic was a 13th century Spanish priest who founded the Dominicans. He and his followers lived an austere and pious lifestyle based on the original apostles lifestyle. Their contemporaries were the Benedictines. Rather than live in a monastery, they went out to the people on the open road. Without money, they would travel on foot from town to town preaching the Gospel. St. Dominic is the patron saint of astronomers. His feast day is August 8th.
Tradition holds that Dominic received the rosary structure from Mary, Mother of God in a vision. The 150 Hail Mary’s are said to honor the 150 psalms in the bible, with 15 decades of ten Hail Mary’s each.
“A man who governs his passions is master of the world. We must either command them, or be enslaved by them. It is better to be a hammer than an anvil.” (anvil in this sense is a heavy iron block)
Archbishop Fulton Sheen said, “The rosary is the book of the blind, where souls see and there enact the greatest drama of love the world has ever known; it is the book of the simple, which initiates them into mysteries and knowledge more satisfying than the education of other men; it is the book of the aged, whose eyes close upon the shadow of this world, and open on the substance of the next. The power of the rosary is beyond description.”
This writeup, A brief history of the Holy Rosary. explains the rosary foundation.