Dietrich von Hildebrand was a German Catholic philosopher and theologian who was called (informally) by Pope Pius XII "the 20th Century Doctor of the Church."
Pope John Paul II greatly admired the work of von Hildebrand, remarking once to von Hildebrand's widow, Alice von Hildebrand, "Your husband is one of the great ethicists of the twentieth century." Pope Emeritus Benedict XVI has a particular admiration and regard for Dietrich von Hildebrand, whom he already knew as a young priest in Munich. In fact, as young Fr. Ratzinger, he even served as an assistant pastor in the church of St. Georg in Munich, which von Hildebrand frequented in the 1950s and 1960s. It was also in St. Georg that Dietrich and Alice von Hildebrand were married.
The degree of Pope Benedict's esteem is expressed in one of his statements about von Hildebrand, "When the intellectual history of the Catholic Church in the twentieth century is written, the name of Dietrich von Hildebrand will be most prominent among the figures of our time." Von Hildebrand was a vocal critic of the changes in the church brought by the Second Vatican Council. He especially resented the new liturgy. Of it he said "Truly, if one of the devils in C.S. Lewis' The Screwtape Letters had been entrusted with the ruin of the liturgy, he could not have done it better."
Von Hildebrand died in New Rochelle, New York, in 1977.
I have some difficulty grasping the full content of philosophical thought and von Hildebrand is a very deep thinker, but I always gain much from his works.
This was pre-Vatican II and so is much more positive. Von Hildebrand was extremely disturbed by the changes in the liturgy, and personally traveled to the Vatican and met with Pope Paul VI to express his dismay and attempt to convince His Eminence to prevent the liturgical changes to no avail. Afterwards, his works exhibited a distressed tone.
This was a life-changing book for me. With great mastery, Dietrich von Hildebrand makes us understand how the space of morality (moral values) can be corrupted and distorted. It's an amazing book that I totally recommend. I would say that it helps to read his "Ethics" book first to get acquainted with his terminology.