Who is Mary?

"Mary, the all-holy ever-virgin Mother of God, is the masterwork of the mission of the Son and the Spirit in the fullness of time. For the first time in the plan of salvation and because his Spirit had prepared her, the Father found the dwelling place where his Son and his Spirit could dwell among men. In this sense the Church's Tradition has often read the most beautiful texts on wisdom in relation to Mary.  Mary is acclaimed and represented in the liturgy as the "Seat of Wisdom." 

"In her, the "wonders of God" that the Spirit was to fulfill in Christ and the Church began to be manifested" (Catechism of the Catholic Church, 721).
Catholic Answers, "Mary" (San Diego: Catholic Answers, www.catholic.com/mary)

Why do Catholics call Mary "The Mother of God?" Is that in the Bible?

One of the best articles we've seen in response to this question is by TIM STAPLES, writing in Catholic Answers Magazine, October 2013. See Mary, Mother of God. [LINK]