Pope Pius XI
Quadragesimo Anno §9
Quadragesimo Anno: On Reconstruction of the Social Order
9 Therefore on the fifteenth day of May, 1891, that long awaited voice thundered forth; neither daunted by the arduousness of the problem nor weakened by age but with vigorous energy, it taught the whole human family to strike out in the social question upon new paths.
Source: Quadragesimo Anno (Vatican.va)