From the 1950s through the late 1970s, Karol Wojtyla (St. John Paul II) was a professor of moral philosophy at the Catholic University of Lublin in Poland, specializing in sexual ethics and what we call today “marriage and family life.”
He produced two important books touching on these matters, The Acting Person, a rigorous philosophical exploration of Christian anthropology, and Love and Responsibility, a much more accessible analysis of love, sex, and marriage.
These texts provided the foundation for the richly textured teaching of St. John Paul II that now goes by the name “theology of the body.”