Absolutely was.
xone:
He was not a Doctor of the Catholic Church. He held a Doctoral Degree in Theology and taught at the Catholic University attached to the Catholic Diocese of his hometown in Germany. A Doctor of the Catholic Church would be Saint Ambrose of Milan, Saint Jerome, Saint Augustine, Saint Thomas Aquinas, etc. In other words, someone the Church recognizes in their writings as being very instrumental in the Church developing its core Doctrine are more formally defining them or making a contribution in the area of Liturgy and Prayer, etc., such as Saint Theresa of Avilla.